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 theydiffer 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 reopresents.

(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

Study the table related to three hydrocarbons A, B, C and answer the questions that follow.

(i) A, Band C are classified as hydrocarbons because

(ii) Which of these organic compounds is an alkyne?

(iii) C₅H₁₀ belongs to

(iv) Identify the incorrect statement about these three hydrocarbons.

(v) General formula for alkane is

(i) Which of the following compounds belong to same homologous series?

(ii) The functional group of compound (R) is

(iii) Compound (T) belongs to homologous series of

(iv) Which of the 'following compounds is unsaturated hydrocarbon?

(v) Which of the following compounds belongs to alkane series?

The table given below shows six organic compounds A, B, C, D, E and F having different molecular formula:

(i) Which of the following compounds belong to same homologous series?

(ii) Which of the following is the member of the same homologous series as E?

(iii) Identify the correct statements.

(iv) Compound B is

(v) Compound (F) has a general formula

A hydrocarbon (P) has the molecular formula C₁₀H₂₂.A hydrocarbon (Q) has two carbon atoms less than (P) and belong to the same homologous series. A hydrocarbon (R) has two carbon atoms more than (P) and belong to the same homologous series.
(i) What is the molecular formula of (Q)?

(ii) To which homologous series do the compound (P), (Q) and (R) belong?

(iii) What is the molecular formula of (R)?

(iv) Identify the correct statement about compounds (P), (Q) and (R).

(v) Compounds (P), (Q) and (R) are

An organic molecule has the following structure:

(i) To which homologous series does this molecule belong?

(ii) What is the general formula of this homologous series?

(iii) Which is the next member of this series?

(iv) Which is the third member of this series?

(v) Which is the second member of this series?

A hydrocarbon is an organic chemical compound composed exclusively of hydrogen and carbon atoms. Hydrocarbons are naturally-occurring compounds and form the basis of crude oil, natural gas, coal, and other important energy sources. Hydrocarbons are highly combustible and produce carbon dioxide, water, and heat when they are burned. Therefore, hydrocarbons are highly effective as a source of fuel.
Study the table related to three hydrocarbons P, Q, R and answer the questions that follow.

(i) P, Q and R are classified as hydrocarbons because
(a) they contain carbon
(b) they contain hydrogen
(c) they contain both carbon and hydrogen
(d) none of these.
P, Q and R are classified as hydrocarbons because these compounds are made up of carbon and hydrogen only.
(ii) Which of these organic compounds is an alkyne?
(a) P (b) Q (c) R (d) Both P and Q
(iii) C₃H₈ belongs to
(a) C_nH_2n+2 series (b) C_nH_2n series (c) C_nH_2n–2 series (d) none of these.
(iv) Identify the incorrect statement about these three hydrocarbons.
(a) All have different general formula.
(b) P, Q both differ by –CH₂ unit.
(c) P is an alkane.
(d) Q is an alkene.
(v) General formula for alkyne is
(a) C_nH_2n (b) C_nH_2n+2 (c) C_nH_2n–2 (d) C_nH_n