A series of organic compounds having same functional group, with similar or almost identical chemical characteristics in which all the members can be represented by the same general formula and the two consecutive members of the series differ by -CH₂ group or 14 mass unit in their molecular formulae is called a homologous series. For example, all the members of alcohol family can be represented by the general formula, C_nH_2n+1 OH where, n may have the values 1, 2, 3, ... etc. The various members of a particular homologous series are called homologues. The physical properties such as density, melting point, boiling point, solubility, etc. of the members of a homologous series show almost regular variation in ascending or descending the series.
(i) Which of the following is not a characteristic of members of a homologous series?

(ii) All the members of homologous series of alkynes have the general formula

(iii) Which of the following statements is not correct?

(iv) Identify the correct statements.
(I) As the molecular mass increases in any homologous series, a gradation in physical properties is seen.
(II) The melting and boiling points decrease with increasing molecular mass.
(III) Other physical properties such as solubility in a particular solvent decreases with increasing molecular mass.
(IV)The chemical properties, which are determined solely by the functional group, remain similar in a homologous series

(v) The table shows the formulae of three organic compounds that belong to the same homologous series.

What is the general formula of this series?

When an element exists in two or more different forms in the same physical state, these different forms are called allotropes and the phenomenon is known as allotropy. Allotropes have similar chemical properties but they differ in their physical properties. Carbon exists in crystalline and amorphous forms. In crystalline form, it occurs as diamond, graphite and fullerenes. Diamond is a colourless, transparent substance having extraordinary brilliance. It is the hardest natural substance known. It is used for cutting marble, granite and glass. Graphite is a greyish-black, opaque substance. It is lighter than diamond i.e., it has lower density. It has sheet like structure having hexagonal layers. One layer slides over the other layer which makes it soft to touch. It is the reason that graphite is used as a lubricant.
(i) Substance X is a moderate conductor of electricity. Substance X has the structure shown below:

Which statements about substance X are correct?
(I) It is a covalent compound.
(II) It has a giant molecular structure.
(III) It has the same structure as graphite
(IV) It has the same structure as diamond

(ii) Which of the following is correct about the structure of diamond?

(iii) Which three allotropes of carbon, do the given figure represents.

(iv) Identify the incorrect statement(s).
(I) Diamond is the hardest substance known while graphite is smooth and slippery.
(II) Diamond is made up of billions of carbon atoms. Each carbon atom is bonded to four other carbon atoms in a tetrahedral manner to form a giant lattice. All carbon atoms are bonded by strong covalent bonds.
(III) Graphite is a poor conductor of electricity unlike other non-metals.
(IV) Graphite has a giant covalent structure that is made up of layers of carbon atoms. In each layer, each carbon atom is bonded to three other carbon atoms to form hexagonal rings of carbon atoms.

(v) Structures Qf two different forms of carbon are given below:

Identify the two forms (I and II respectively) and how are they related to each other?

As neutral atom carbon has electronic configuration K L. To gain inert gas configuration carbon can either 2, 4 donate 4 valence electrons (helium gas configuration) or gain 4 electrons (neon gas configuration), but it cannot do so. To acquire inert gas configuration carbon can only share its 4 valence electrons with other atoms forming covalent bonds. A covalent bond can be defined as a chemical bond formed between two atoms by mutual sharing of valence electrons so that each atom acquires the stable electronic configuration of the nearest noble gas. The concept of covalent bonds was given by Langmuir and Lewis to explain bonding in non-ionic compounds. The covalent bonds are of three types. If each atom contributes one electron, the covalent bond formed is called a single covalent bond and is represented by a single line (-) and if each atom contributes two electrons, the covalent bond formed is called a double bond and is represented by a double line (=) and if each atom contributes three electrons, the covalent bond formed is called a triple bond and is represented by a triple line (=).
(i) Which of the following do not contain a double bond?
I. S02
II. NH3
III. HCl
IV. 02

(ii) Which of the following contains a triple bond?

(iii) The shared pair of electrons is said to constitute a _______________ bond between two hydrogen atoms.

(iv) Which of the following molecules has all its atoms joined together by double covalent bonds?

(v) Chlorine forms a diatomic molecule, Cl₂ . The electron dot structure for this molecule is

Two allotropic forms of carbon which are crystalline in nature, are diamond and graphite. They differ physically but chemically they are similar. Diamond is the hardest crystalline form of carbon. In diamond, each carbon atom is linked to four other carbon atoms by covalent bonds. In graphite, each carbon atom is linked to three other carbon atoms by covalent bond. Graphite is relatively soft and greasy. It is also a good conductor of electricity. The C-C bond length in graphite is 141.5 pm while in diamond it is 154 pm.
(i) Which of the following is a good conductor of heat and electricity?

(ii) Graphite is a good conductor of electricity because

(iii) Which of the following types of binding forces is present in the structure of diamond?

(iv) Diamond is not a good conductor of electricity because

(v) Which of the following is the structure of diamond?

The compounds which have the same molecular formula but differ from each other in physical or chemical properties are called isomers and the phenomenon is called isomerism. When the isomerism is due to difference in the arrangement of atoms within the molecule, without any reference to space, the phenomenon is called structural isomerism. In other words, structural isomers are compounds that have the same molecular formula but different structural formulas, i.e., they are different in the order in which different atoms are linked. In these compounds, carbon atoms can be linked together in the form of straight chains, branched chains or even rings.
(i) Which of the following sets of compounds have same molecular formula?

(ii) In order to form branching, an organic compound must have a minimum of

(iii) Which of the following is an isomeric pair?

(iv) Among the following the one having longest chain is

(v) The number of isomers of pentane is