NEET Chemistry: The s-Block Elements questions with solutions

Q1. Compare the physical properties of metals and non-metals in general with reference to malleability.

1. Both are malleable
2. None are malleable
3. only metals are malleable
4. only non-metals are malleable

Answer: only metals are malleable

Metals are generally malleable because their atoms can slide past one another without the structure breaking. Non-metals are usually brittle, so they do not show malleability in general.

Q2. Which of one of the following burns in the air giving a gaseous oxide? (at room temp.)

1. Hydrogen
2. Sodium
3. sulphur
4. Helium

Answer: Sodium

Sodium is a highly reactive metal and burns in air, producing sodium oxide/peroxide, which are oxides formed from combustion. Hydrogen burns too, but it forms water rather than a gaseous oxide in this context; helium is inert, and sulphur is a nonmetal that forms sulfur dioxide.

Q3. Ionic mobility of which of the following alkali metal ions is lowest when aqueous solution of their salts are put under an electric field?

1. (a) K
2. (b) Rb
3. (c) Li
4. (d) Na

Answer: (c) Li

The ionic mobility of Li+ is the lowest because it has the smallest ionic radius among alkali metals, leading to the strongest hydration and the largest effective size in aqueous solution, which reduces its mobility.

Q4. Identify the alloy containing a non-metal as a constituent in it.

1. Invar
2. Steel
3. Bell metal
4. Bronze

Answer: Steel

Steel contains carbon, which is a non-metal, as one of its constituents. The other options do not include a non-metal as a component.

Q5. Mg is present in which of the following?

1. (a) Starch
2. (b) Chlorophyll
3. (c) Both
4. (d) None

Answer: (b) Chlorophyll

Magnesium (Mg) is a central component of the chlorophyll molecule, which is essential for photosynthesis. It is not present in starch.

Q6. Among the following oxides, the one which is most basic is:

1. ZnO
2. MgO
3. Al2O3
4. N2O5

Answer: MgO

MgO is the most basic among the given oxides because it is an alkaline earth metal oxide, which is strongly basic in nature. The others are either amphoteric (ZnO, Al2O3) or acidic (N2O5).

Q7. When a substance A reacts with water, it produces a combustible gas B and a solution of substance C in water. When another substance D reacts with this solution of C, it also produces the same gas B on reaction with dilute sulphuric acid at room temperature. A imparts a deep golden yellow colour to a smokeless flame of Bunsen burner. A, B, C and D respectively are

1. Na, H2, NaOH, Zn
2. K, H2, KOH, Al
3. Ca, H2, Ca(OH)2, Sn
4. CaC2, C2H2, Ca(OH)2, Fe

Answer: Na, H2, NaOH, Zn

Substance A is sodium (Na), which reacts with water to produce hydrogen gas (B) and sodium hydroxide (C). Zinc (D) reacts with sodium hydroxide to release hydrogen gas. Sodium imparts a golden yellow color to a flame, confirming the identification.

Q8. The number of hydrogen bonded water molecules(s) associated with CuSO4·5H2O is

1. 5
2. 3
3. 1
4. 2

Answer: 3

In CuSO4·5H2O, two water molecules are coordinated to the Cu²⁺ ion, and the remaining three water molecules are hydrogen-bonded to the sulfate ion.

Q9. Calgon used as a water softener is

1. (a) Na2[Na4(PO3)6]
2. (b) Na4[Na2(PO4)6]
3. (c) Na4[Na4(PO4)5]
4. (d) Na4[Na2(PO4)6]

Answer: (a) Na2[Na4(PO3)6]

Calgon, a water softener, is chemically represented as Na2[Na4(PO3)6], which is a complex phosphate used to remove calcium and magnesium ions from hard water.

Q10. The following metal ion activates many enzymes, participates in the oxidation of glucose to produce ATP and with Na, is responsible for the transmission of nerve signals.

1. Copper
2. Calcium
3. Potassium
4. Iron

Answer: Potassium

Potassium (K⁺) is essential for enzyme activation, ATP production during glucose oxidation, and works with sodium (Na⁺) in nerve signal transmission.

Q11. Which one of the alkali metals forms only the normal oxide, M2O, on heating in air?

1. Rb
2. K
3. Li
4. Na

Answer: Li

Lithium (Li) forms only the normal oxide (Li2O) when heated in air due to its small size and high charge density, which stabilizes the oxide ion (O2-). Other alkali metals form peroxides or superoxides under similar conditions.

Q12. The ease of adsorption of the hydrated alkali metal ions on an ion-exchange resin follows the order:

1. Li+ < K+ < Na+ < Rb+
2. Rb+ < K+ < Na+ < Li+
3. K+ < Na+ < Rb+ < Li+
4. Na+ < Li+ < K+ < Rb+

Answer: Rb+ < K+ < Na+ < Li+

The ease of adsorption of hydrated alkali metal ions depends on their hydration enthalpy, which decreases as the size of the ion increases. Thus, smaller ions like Li+ are more strongly hydrated and less easily adsorbed, while larger ions like Rb+ are less hydrated and more easily adsorbed.

Q13. Which of the alkali metal chloride (MCl) forms its dihydrate salt (MCl·2H2O) easily?

1. KCl
2. LiCl
3. CsCl
4. RbCl

Answer: LiCl

Lithium chloride (LiCl) forms its dihydrate salt (LiCl·2H2O) easily due to its high hydration enthalpy, which is a result of the small size and high charge density of the lithium ion.

Q14. HCl was passed through a solution of CaCl2, MgCl2, and NaCl. Which of the following compound(s) crystallise(s)?

1. Only NaCl
2. Only MgCl2
3. NaCl, MgCl2 and CaCl2
4. Both MgCl2 and CaCl2

Answer: Only NaCl

When HCl is passed through the solution, NaCl crystallizes because it is less soluble in concentrated HCl compared to MgCl2 and CaCl2, which remain dissolved due to their higher solubility.

Q15. Crude sodium chloride obtained by crystallisation of brine solution does not contain

1. CaSO4
2. MgSO4
3. Na2SO4
4. MgCl2

Answer: Na2SO4

Crude sodium chloride obtained from brine typically contains impurities like CaSO4, MgSO4, and MgCl2, but not Na2SO4, as sodium sulfate is not a common impurity in this process.

Q16. Which of the following statements is incorrect?

1. Pure sodium metal dissolves in liquid ammonia to give blue solution.
2. NaOH reacts with glass to give sodium silicate
3. Aluminium reacts with excess NaOH to give Al(OH)3
4. NaHCO3 on heating gives Na2CO3

Answer: Aluminium reacts with excess NaOH to give Al(OH)3

The incorrect statement is C. Aluminium reacts with excess NaOH to form sodium aluminate (Na[Al(OH)4]), not Al(OH)3. Al(OH)3 is formed only in limited NaOH.

Q17. In Castner-Kellner cell for production of sodium hydroxide:

1. Brine is electrolyzed with Pt electrodes
2. Brine is electrolyzed using graphite electrodes
3. Molten sodium chloride is electrolyzed
4. Sodium amalgam is formed at mercury cathode

Answer: Sodium amalgam is formed at mercury cathode

In the Castner-Kellner cell, brine is electrolyzed, and sodium amalgam is formed at the mercury cathode, which reacts with water to produce sodium hydroxide.

Q18. Which of the following is known as fusion mixture?

1. Mixture of Na2CO3 + NaHCO3
2. Na2CO3·10H2O
3. Mixture of K2CO3 + Na2CO3
4. NaHCO3

Answer: Mixture of K2CO3 + Na2CO3

Fusion mixture is a combination of potassium carbonate (K2CO3) and sodium carbonate (Na2CO3), used in qualitative analysis to fuse samples for testing acidic radicals.

Q19. Enzymes that utilize ATP in phosphate transfer require an alkaline earth metal (M) as the cofactor. M is:

1. Be
2. Mg
3. Ca
4. Sr

Answer: Mg

Magnesium (Mg) is the alkaline earth metal that acts as a cofactor for enzymes utilizing ATP in phosphate transfer, as it stabilizes the negative charges on ATP.

Q20. Which of the following oxides is most acidic in nature?

1. MgO
2. BeO
3. CaO
4. BaO

Answer: BeO

BeO is the most acidic among the given oxides because it is amphoteric, while the others (MgO, CaO, BaO) are basic in nature. The acidic character decreases down the group in alkaline earth metals.