Question 1

Which of the following is a functional group present in ethanol (C₂H₅OH)?

Accepted Answer

Ethanol has the molecular formula C₂H₅OH. The -OH group attached to a carbon atom is called a hydroxyl group or alcohol functional group. This is the defining characteristic of alcohols in organic chemistry. According to NCERT Class 10, alcohols contain the -OH functional group bonded to a saturated carbon atom. Ethanol is the simplest alcohol after methanol and is widely used as a solvent and fuel.

Question 2

Ethane (C₂H₆) and ethene (C₂H₄) are two carbon compounds. Which of the following statements correctly distinguishes them based on their bonding and chemical properties?

Accepted Answer

Ethane (C₂H₆) contains a single C–C covalent bond (saturated hydrocarbon), while ethene (C₂H₄) contains a double C=C covalent bond (unsaturated hydrocarbon). This structural difference makes ethene more reactive. Ethene undergoes addition reactions (e.g., with bromine water, turning it colourless), whereas ethane does not readily undergo addition reactions under normal conditions. Both are members of homologous series (alkanes and alkenes respectively), but they differ fundamentally in saturation and reactivity. According to NCERT Class 10 Chemistry, unsaturated hydrocarbons (containing C=C or C≡C bonds) are more reactive than saturated hydrocarbons because the double or triple bond can be broken to add other atoms. Therefore, answer is B.

Question 3

Which allotrope of carbon has a layered structure where each carbon atom is bonded to three other carbon atoms, making it a good conductor of electricity?

Accepted Answer

In graphite, each carbon atom is sp2-hybridized and forms covalent bonds with three neighbouring carbon atoms in a hexagonal layered structure. The fourth valence electron of each carbon is delocalized across the layers, forming a 'sea' of mobile electrons. This free movement of electrons makes graphite a good conductor of electricity — a property absent in diamond, where all four electrons are locked in covalent bonds with no free electrons.

Question 4

Ethene (C₂H₄) undergoes an addition reaction with bromine water, producing a colourless dibromide product. Which of the following correctly identifies both the type of reaction and the structural reason why this reaction occurs?

Accepted Answer

This question tests understanding of unsaturated carbon compounds and addition reactions at NCERT Class 10 level. Ethene contains a C=C double bond (π-bond), which is electron-rich and reactive. When bromine water is added, the π-electrons attack the bromine molecule, breaking the C=C double bond and forming two new C-Br single bonds. This is an addition reaction because atoms are added across the double bond without loss of any atoms. The structural reason is that the π-bond (pi-bond) in the C=C double bond is weaker and more reactive than σ-bonds (sigma-bonds), making it susceptible to electrophilic attack by bromine. The product is 1,2-dibromethane (BrCH₂-CH₂Br), which is colourless. The decolourization of bromine water is a characteristic test for unsaturation in organic compounds. Therefore, the answer is **B** — Addition reaction; the C=C double bond (π-bond) is electron-rich and reactive.

RRB Group D Carbon Compounds

Carbon Compounds— Rules & Concept

Key Points to Remember

Exam-Specific Tips

Carbon Compounds — Practice Questions

60-Second Revision — Carbon Compounds