#### Abstract

Graph theory is a subdivision of discrete mathematics. In graph theory, a graph is made up of vertices connected through edges. Topological indices are numerical parameters or descriptors of graph. Topological index tells the symmetry of compound and helps us to compare those mathematical values, with boiling point, melting point, density, viscosity, hydrophobic surface area, polarity, etc., of that compound. In the present research paper, degree-based topological indices of Zeolite Socony Mobil-5 are calculated. Names of those topological indices are Randić index, first Zagreb index, general sum connectivity index, hyper-Zagreb index, geometric index, ABC index, etc.

#### 1. Introduction

In graph theory, the term graph was suggested in eighteenth century by Leonhard Euler (1702–1782). He was a Swiss mathematician. He manipulated graphs to solve Konigsberg bridge problem [1–3]. Chemical graph theory is a topological division of mathematical chemistry that practices graph theory to model chemical structures mathematically. It studies chemistry and graph theory to view the detailed physical and chemical properties of compounds. A graph *G* = is comprised through a set of vertices *V* and an edges set [4].

Topological indices study the properties of graphs that remain constant/unchanged after continuous change in structure. Topological indices explain formation and symmetry of chemical compounds numerically and then help in advancement of QSAR (qualitative structure activity relationship) and QSPR (quantitative structure property relationship). Both QSAR and QSPR are used to build a relation among molecular structure and mathematical tools. These descriptors are helpful to correlate physio-chemical properties of compounds (enthalpy, boiling and melting point, strain energy, etc.) that is why these descriptors have a large number of applications in chemistry, biotechnology, nanotechnology, etc.

Topological indices are invariants of graph that is why topological indices are independent of pictorial representation of graph. In other words, it is a numerical value that describes the structure of chemical graph [5, 6]. Among the three types of topological indices, degree-based indices have great importance. The need to define these indices is to explain physical properties of every chemical structure with a number. Continuous change in shape does not affect the value of topological index. Topological indices are useful in the study of QSAR and QSPR because topological indices show the physical properties and convert the chemical structure into a numerical value.

Distance-based topological indices deal with distances of graph, degree-based topological indices use the concept of degree, and counting-based topological index depends upon counting the edges. Randic explained some characteristics of a topological index. Some of them are explained here.

A topological index should(i)have architectural interpretation(ii)be well-defined(iii)be related with at least one physio-chemical property of compound(iv)be uncomplicated(v)display an appropriate size dependence(vi)modify with modification in structure(vii)locally defined(viii)have related with other indices

Topological indices show translations of chemical compounds into distinctive structural descriptors as a numerical value that can be used by QSAR [7, 8]. Topological indices are awfully beneficial in describing the properties of given compound. Chemists can use these indices to correlate considerable range of characteristics. Medicine industry is developing new drug designs that are useful for humans, plants, and animals. Many graph theoretical techniques have been established for forecasting of medicinal, environmental, and physio-chemical properties of compounds. It is not astonishing to see such a great victory of graph theory and topological indices in analyzing biological and physical characteristics of chemical compounds.

##### 1.1. ZSM

Zeolites (alumino silicate) are tetrahedrally-linked structures based on silicate and aluminate tetrahedral. Structural chemistry deals with the framework of zeolites; it also works out on the arrangement of cations and other molecules in pore spaces. It belongs to a pentasil class of zeolite. It consists of silica (Si) and alumina (Al). It is named as ZSM-5 due to pore diameter of five angstrom; also, it has Si/Al ratio of five [9]. Size of the molecule depends on the type of structure. It is a crystalline powder. Geometry of pores can be connected in channels in one, two, or three dimensions.

###### 1.1.1. Motivations

The structure of ZSM-5 has great importance in the field of chemistry, petroleum, and medicine industry. ZSM-5 is useful because of its stability, favorable selectivity, metal tolerance, and flexibility. It is also useful for the treatment of fertilizers. It helps to separate oxygen and nitrogen in the air. This unique structure is useful in petroleum industry as a catalyst. It is generally used in the conversion of methanol to gasoline as well as refining of oil. Through dehydration, it changes alcohol into petrol. Efficiency of LPG can also be increased through ZSM-5 catalyst. It keeps unusual hydrophobicity that is useful to separate hydrocarbons from polar compounds. Basic reason of calculation of topological indices is the industrial uses of ZSM-5 structure.(1)*First General Zagreb Index*. This index was first presented by Li and Zhao. Its mathematical form is defined in [10–12] as follows: *First and Second Zagreb Index.* There are two Zagreb groups of indices, denoted by and [13–15]. Both of these indices are explained in 1970s by Gutman and Tranjistic.(2)*First Zagreb Index*. It is defined in [16, 17]:(3)*Second Zagreb Index.* It is defined in [11, 16]: Multiple and polynomial Zagreb indices: In 2012, new kinds of Zagreb indices were introduced by Ghorbani and Azimi, named as first and second multiple Zagreb indices represented as and [11, 15, 18]. The polynomials are used to find the Zagreb index. First and second Zagreb polynomial indices are written as and .(4)First and second multiple Zagreb indices:(5)First and second polynomial Zagreb indices:(6)*Hyper-Zagreb Index.* Modified Zagreb index is called hyper-Zagreb and that was introduced in 2013 by Shirdil, Rezapour, and Sayadi [19–21], mathematically written as(7)Second modified Zagreb index:(8)*Reduced second Zagreb index.* This index was proposed by Furtula and it is defined as(9)*Atom Bond Connectivity Index.* It was written in 1998 by Ernesto Estrada and Torres [15, 22–24]. It is used to model thermodynamic characteristics of organic compounds (especially alkanes). Mathematically,(10)*Fourth Atom Bond Connectivity Index*. In 2010, Ghorbani et al. introduced this index [13, 14]. It is written as index:(11)*General Randić Connectivity Index*. First degree-based TI was proposed in 1975 by Millan Randić. At that time, it was called as branching index [8, 17, 18] and used to measure the branching of hydrocarbons. In 1998, Eddrös and Bollobás wrote the general term of this index by changing the factor with [25]. It is defined as the total sum of weights of all the edges , is the degree of , is the degree of *q,* and .(12)Randić index: This index can also be called as first genuine degree-based topological index [15, 23]. Randić index is defined as(13)*Reciprocal Randić Index.* This index was first studied by Favaron, Mahéo, and Saclé [26]. The index is helpful in modeling of boiling points of hydrocarbons. It is defined as(14)*Reduced Reciprocal Randić Index*. It is the analogue of reciprocal Randić index [26, 27]. It is defined as follows:(15)*Geometric Arithmetic Index.* GA index was proposed by Vukicevic̀ and Furtula [6, 14, 15]; it is stated as(16)*Fifth Geometric Arithmetic Index.* In 2011, Grovac et al. introduced this index [7]. Mathematically, it is written as(17)*Forgotten Index*. This index was given by Gutman and Furtula in 2015 [16, 28, 29]. It is denoted by *F* (*G*) or *F* index:(18)*General Sum Connectivity Index*. The index was proposed by Zhou and Trinajstić [15, 23, 30]. Mathematically, where .(19)*Symmetric Division Index*. In 2010, Vukicevic̀ and Furtula proposed this useful index denoted by SD (*G*) [28, 31, 32]:(20)*Harmonic Index*. Siemion Fajtlowicz wrote a computer program that works for the automatic generation of conjectures in graph theory [11, 15]. He also examined the relationship between graph invariants; while doing this work, he found a vertex degree-based quantity. Later on, (in 2012) Zhang rediscovered that unknown quantity and named it as harmonic index. It is written as

#### 2. Topological Indices of ZSM-5 Graphs

Topological indices remain constant for a given compound; they do not depend on the direction or position of graph. We can predict many physical properties of compounds such as solubility, soil sorption, boiling and melting properties, biodegradability, toxicity, vaporization, and thermodynamic properties.

##### 2.1. Description of ZSM-5 Graph

The graph of ZSM-5 is given in Figure 1 and it is represented by . There are vertices and edges in .

Theorem 1. *Let be a graph of ZSM-5. Then, first general Zagreb index is*

*Proof. * is given in Figure 1. There are vertices, of degree 2 vertices, and of degree 3 vertices.

Also, is defined as (1):We get by using the following formula:

Theorem 2. * is the graph of ZSM-5. First Zagreb index is as follows:*

*Proof. *Assume is a graph of ZSM-5. Then, is cleaved into 3 classes. The edges group contains edges , and . The class has edges; here, , . The arc division has arcs ; here, , .It is easily understood thatWe define in equation (29) as

Theorem 3. * is a graph of ZSM-5 and its 1st and 2nd polynomial Zagreb index is*(1)*;*(2)

*Proof. * is a graph of ZSM-5. is divided into three parts.

has edges , has arcs , and keeps arcs and .

By using the definition of in equation (6):From (3), we havewhich completes the proof.

Theorem 4. *First and second multiple Zagreb index of of ZSM-5 is given as*(1)*;*(2)

*Proof. * is classified into 3 edge classes based on the degree of end vertices. has edges , where . contains edges , where , . contains edges , where , . Also consider , , and . We define as (4):Now, we define as (5):which completes the proof.

Theorem 5. *Then, hyper-Zagreb of is written as follows:*

*Proof. * is divided into 3 edge divisions based on the degree of end vertices. holds edges , where . holds edges , where , . holds edges , where , . ,Since, we have (8),which completes our proof.

Theorem 6. * is the graph of ZSM-5. The second modified Zagreb index is given as*

*Proof. *Consider to be a graph of ZSM-5. is divided into 3 sets based on the degree of end vertices. contains edges , where . holds edges , where , . holds edges , where , . , , and .

We know the definition of as (9):

Theorem 7. *Let be the graph of ZSM-5. Then, reduced second Zagreb index is*

*Proof. *Assume to be a graph of ZSM-5. is divided into parts. holds edges , where . has lines , where , . holds lines , where , . Also consider From equation (10), we have the definition of reduced second Zagreb index:

Theorem 8. *Atom bond connectivity index of of ZSM-5 is as follows:*

*Proof. * is our graph of ZSM-5. is divided into three edge groups. holds edges , . keeps number of lines , and . has lines , where . We define ABC(*G*) in (11):

Theorem 9. *ABC-4 index of ZSM-5 is as follows:*

*Proof. *ZSM-5 has 36*pq* + 2*p* − 2*q* number of edges.

Consider an arc set relies on degree summation of neighbors of end vertices and is divided into nine disjoint groups of edges, such as holds number of edges , where , has 4 lines , where and , has edges , where and , has edges , where and , contains edges , where and , holds lines , where and , consists of number of arcs , where , has lines , where and , and contains number of edges , where . The index is defined in equation (12):After putting the values of , we getand after simplification,

Theorem 10. *Let be the graph of ZSM-5. Fifth generation geometric arithmetic index is as follows:*

*Proof. *ZSM-5 has 36*pq* + 2*p* − 2*q* number of edges.

Consider an arc set relies on degree summation of neighbors of end vertices and is divided into nine disjoint groups of edges, such as holds number of edges , where , has 4 lines , where and , has edges , where and , has edges , where and , contains edges , where and , holds lines , where and , consists of number of arcs , where , has lines , where and , and contains number of edges , where . The index is defined in equation (18):After putting the values , we getAfter simplification,

Theorem 11. *Let be the graph of ZSM-5. Then, general Randic connectivity index is as follows:*

*Proof. *The graph of zeolite encounters edges and vertices.

The numeral of vertices of degree 2 are and of degree 3 are . of are . is divided into three edge groups. has edges , where , contains edges , where and , and supports arcs , where .

By using definition of Randić index (13),Now, we haveAfter simplification, we get

Theorem 12. *Let be the graph of ZSM-5. Then, the reciprocal Randić index is as follows:*

*Proof. *The graph of zeolite encounters edges and vertices.

The numeral of vertices of degree 2 are and of degree 3 are . of are . cleaves into three disunite edge groups: has arcs , where , contains edges , where and , and supports arcs , where .

We define this index in equation (16):

Theorem 13. *Consider to be the graph of ZSM-5. Geometric arithmetic index is described as follows:*

*Proof. *The graph of zeolite encounters edges and vertices. The grouping of the vertices is given as follows:

The vertices of degree two are and of degree three are . Cardinality of of is . The arc group cleaves in 3 disjoint arc groups that rely on the degrees of the end vertices, such as has lines , where . has lines , where and . supports lines , where .We define this index in equation (17) as

Theorem 14. *Forgotten index of graph of ZSM-5 is as follows:*

*Proof. *The graph encounters edges and vertices.

The points of degree 2 are and the points of degree 3 are . The cardinality edge group of is . cleaves into three disjoint line groups that are as follows: holds arcs and . supports arcs , where and , and has arcs , where .

By using the definition of forgotten index (19),

Theorem 15. *Let be the graph of ZSM-5, then the general sum connectivity index is as follows:*

*Proof. *The graph of zeolite encounters edges and vertices.

Vertices of degree two are and of degree three are . of are . cleaves into 3 disjoint edge groups. holds edges , where , holds edges , where and , holds edges , where . From (20), we get the definition of general sum connectivity index:

Theorem 16. * is the graph of ZSM-5 and its symmetric division index is as follows:*

*Proof. * of zeolite encounters edges and vertices.

The number of vertices of degree two are and the number of vertices of degree 3 are . of are . cleaves into three disjoint edge groups. holds edges , where , holds edges , where and , and holds