Answer:
1. Answer : (d) It has a polymeric structure
Explanation: Red phosphorus is believed to have long chains of P4 tetrahedrons, i.e., it is highly polymerized and hence is less reactive.
2. Answer : (c) Reaction between Zn and conc. H2SO4
Explanation: Concentrated sulphuric acid reacts with Zn to give SO2 and not H2
3. Answer : (d) Strongly heating the solid
Explanation: Oxygen gas can be prepared from solid KMnO4 250°C
2KMnO4 → KMnO4 + MnO2 + O2
4. Answer : (b) By action of ultraviolet rays on oxygen molecule
Explanation: In the upper layer of atmosphere, the Ultraviolet rays (UV rays) split the molecule of oxygen (O2) nto its constituent 2 atoms. Each of the atom then combine with another oxygen (O2) molecule which give O3
5. Answer : (c) 2, 4
Explanation: The tendency to form +2 ionic state increase on moving down the group due to inert pair effect. Most characteristic oxidation state for lead and tin are +2,+4 respectively.
6. Answer : (a) The oxygen-oxygen bond length in ozone is identical with that of molecular oxygen
Explanation: Due to resonance the bond order in ozone is 1.5, hence O−O bond length in O3 > O−O bond length in O2
7. Answer : (d) Quick lime
Explanation: Quicklime (CaO) is used for drying NH3 gas because bothare basic, do not react. On the other hand, H2SO4 and P2O5 are acidic, reacts with ammonia forming salts. CaCl2 forms complex with ammonia.
8. Answer : (b) Lewis Acids
Explanation: The boron atom in trihaldies has only six electrons in the valence shell and hence can accept a pair of electrons in the vacant p-orbital to complete its octet. As a result, boron trihaldie act as a Lewis acids.
9. Answer : (a) Increase to 1.5 times
Explanation: 1 mole of O3 on heating produces 1 mole of O2 and 1 mole of [O], hence its volume increases to 1.5 times.
10. Answer : (c) Aluminum
Explanation: Aluminum is an excellent conductor of heat and electricity. Its thermal conductivity is about one-half that of copper; its electrical conductivity, about two-thirds.
11. Answer : (c) Amphoteric oxide
Explanation: Aluminium oxide is amphoteric. It has reactions as both a base and an acid. Reaction with water: Aluminum oxide is insoluble in water and does not react like sodium oxide and magnesium oxide.
12. Answer : (a) Aluminium
Explanation: Aluminium is the most abundant metal and third most abundant element in earth's crust.
13. Answer : (a) Low density
Explanation: Due to the low density of aluminium it is useful for food packaging.
14. Answer : (a) Boron
Explanation: When we mmove down the group, the IE decreases, the electropositive character, hence the metallic character also increases.
15. Answer : (a) Ga
Explanation: The m.p decreases from B to Ga , hence gallium (Ga) has least m.p. (303 K) among group of 13 element.
16. Answer : (a) of inert pair effect
Explanation: Thallium shows different (+1 and +3) oxidation states because of inert pair effect.
17. Answer : (a) B
Explanation: Boron does not react with aqueous NaOH, However, it forms borates when fused with alkalies.
18. Answer : (a) the presence of hydrogen bondstry
Explanation: In Boric acid each B atom is sp2 hybridized and contains BO-33 units which are held together by hydrogen bonds.
19. Answer : (a) Aluminum
Explanation: Bauxite is also known as aluminum ore and contains aluminum bearing minerals.
20. Answer : (b) 8
Explanation: In the diamond cubic unit cell, there are eight corner atoms, six face centered atoms and four more atoms inside the structure.
∴ Number of atoms present in a diamond cubic unit cell
=1 + 3 + 4
= 8 atoms
21. Answer : (b) Pyrosilicate
Explanation: In pyrosilicates, there is only one shared oxygen, in linear chain silicates, two oxygen per tetrahedra are shared while in three-dimensional silicates, all four oxygens are shared.
22. Answer : (a) Al
Explanation: Aluminium is protected from corrosion by a layer of its own oxide Al2O3.
23. Answer : (a) Al
Explanation: The Hoopes process is a metallurgical process, used to obtain the aluminium metal of very high purity.
24. Answer : (c) If assertion is true but reason is false
Explanation: Al metal is rendered passive when treated with conc. HNO3 because concentrated HNO3 is oxidising agent and produces a protective layer of oxide on the surface.
25. Answer : (b) Ferric oxide and aluminium powder
Explanation: The powder consists of aluminum and the oxide of a metal such as iron. When ignited or heated, it gives off an enormous amount of heat as a result of the chemical combination of the aluminum with the oxygen of the oxide.
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