1. Consider the chemical reaction given as:
–CO (g) + — H2(g) → — C8H18(l) + — H2O.
This equation can be balanced by inserting the following in blank spaces:

Answer: a) 8, 2, 1, 17

Explanation: This reaction represents the synthesis of octane (C8H18) from carbon monoxide (CO) and hydrogen gas (H2). The correct coefficients to balance this equation are 8 for CO, 2 for H2, 1 for C8H18, and 17 for H2O.

2. In an alpha scattering experiment, few alpha particles rebounded because:

Answer: c) All the positive charge and mass of the atom is concentrated in a small volume

Explanation: In Rutherford’s alpha scattering experiment, alpha particles were deflected by the nucleus of atoms. This happens because the mass and positive charge of the atom are concentrated in a tiny region called the nucleus. When alpha particles approach the nucleus, they experience a strong repulsion, causing some of them to bounce back.

3. Consider the reactions given below. On the basis of these reactions, find out which of the algebraic relations given in options (i) to (iv) is correct?
C (g) + 4 H (g) → CH4(g); ΔrH = x kJ/mol
C (graphite,s) + 2 H2(g) → CH4(g); ΔrH = y kJ/mol

Answer: d) x > y

Explanation: The reaction C (g) + 4 H (g) → CH4(g) involves gaseous carbon and hydrogen atoms. The second reaction involves graphite (solid carbon) and hydrogen gas to form methane. Since gaseous carbon atoms are less stable than graphite (solid form), the enthalpy change (ΔrH) for the formation of CH4 from gaseous carbon and hydrogen will be greater (less negative) than from solid graphite and hydrogen.

4. Give the number of electrons in the species, O2 and O+2.

Answer: b) 16 and 14

Explanation: O2 has 16 electrons (8 from each oxygen atom). O+2 has lost two electrons due to the positive charge, so it has 14 electrons.

5. Which of the following always has a negative value?

Answer: d) Heat of combustion

Explanation: Heat of combustion refers to the heat released when a substance undergoes complete combustion. This process is always exothermic, meaning it releases energy, and thus has a negative value.

6. What will be the electronic configuration of the element with atomic number 24?

Answer: None of the options

Explanation: The correct electronic configuration for the element with atomic number 24 (Chromium, Cr) is: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s². This configuration follows the rule of maximum stability where 3d is half-filled before 4s.

7. On the reaction 2Ag + 2H2SO4 → Ag2SO4 + 2H2O + SO2, sulphuric acid acts as an?

Answer: d) An acid as well as an oxidant

Explanation: Sulfuric acid (H2SO4) acts as an acid because it donates protons (H+), and it also acts as an oxidizing agent, causing the reduction of silver (Ag) to silver sulfate (Ag2SO4).

8. The reaction CH3CH=CH2 + HBr → CH3CH2CH2Br can be explained by:

Answer: b) Free-radical mechanism

Explanation: This is a typical electrophilic addition reaction, which follows a free-radical mechanism. The double bond reacts with HBr, leading to the formation of a carbocation intermediate that then reacts with Br-.

9. The chemical reaction that represents the reduction of nitrogen is:

Answer: a) N2 + 3H2 → 2NH3

Explanation: The reduction of nitrogen occurs when nitrogen gas (N2) reacts with hydrogen gas (H2) to form ammonia (NH3). This is a well-known reaction called the Haber process, where nitrogen is reduced from its elemental form to ammonia.

10. Which of the following elements has the highest ionization energy?

Answer: d) Neon

Explanation: Ionization energy is the energy required to remove an electron from an atom. Neon, being a noble gas, has a stable electronic configuration, and its high ionization energy is due to the strong attraction between its electrons and the nucleus, making it harder to remove an electron compared to other elements.

11. The molar mass of a gas is given as 32g/mol. What is the mass of 1.5 moles of this gas?

Answer: b) 48 g

Explanation: The mass of 1 mole of the gas is 32 g. Therefore, the mass of 1.5 moles of the gas is 1.5 * 32 = 48 g.

12. Which of the following reactions is an example of a redox reaction?

Answer: d) All of the above

Explanation: A redox (reduction-oxidation) reaction involves the transfer of electrons. All three of these reactions involve the transfer of electrons, making them redox reactions. For example, in the reaction H2 + O2 → H2O, hydrogen is oxidized (losing electrons) and oxygen is reduced (gaining electrons).

13. What is the name of the compound with the formula NaOH?

Answer: b) Sodium hydroxide

Explanation: NaOH is a strong base known as sodium hydroxide. It is commonly used in cleaning products and is known as lye.

14. Which of the following acids is present in vinegar?

Answer: a) Acetic acid

Explanation: Vinegar is an aqueous solution of acetic acid (CH3COOH), which gives it its characteristic sour taste and odor.

15. In a reaction between an acid and a base, what is typically produced?

Answer: a) Salt and water

Explanation: When an acid reacts with a base, a neutralization reaction occurs, producing salt and water. For example, HCl + NaOH → NaCl + H2O.

16. Which of the following is the correct representation of the noble gas configuration for helium?

Answer: a) 1s²

Explanation: The noble gas configuration for helium (He) is 1s², meaning it has two electrons in its first and only energy level.