Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions for Chemistry

Read the passage given below and answer the following question:

The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.

In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

Assertion: Cations of transition elements occur in various valence states.

Reason: Large number of oxides of transition elements are possible.

Read the passage given below and answer the following question:

The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.

In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

Assertion: Crystal structure of oxides of transition metals often show defects.

Reason: Ligand field effect cause distortions in crystal structures.

Read the passage given below and answer the following question:

The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.

In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

Assertion: Transition metals form protective oxide films.

Reason: Oxides of transition metals are always stoichiometric.

The lattice site in a pure crystal cannot be occupied by ______.

Extent of physisorption of a gas increases with ______.

Which of the following is not a favourable condition for physical adsorption?

Physical adsorption of a gaseous species may change to chemical adsorption with ______.

In physisorption adsorbent does not show specificity for any particular gas because ______.

In which of the following reactions heterogenous catalysis is involved?

(a) \[\ce{2SO2 (g) + O2 (g) ->[NO(g)] 2SO3 (g)}\]

(b) \[\ce{2SO2 (g) ->[Pt(s)] 2SO3 (g)}\]

(c) \[\ce{N2 (g) + 3H2 (g) ->[Fe(s)] 2NH3 (g)}\]

(d) \[\ce{CH3COOCH3 (l) + H2O (l) ->[HCI(l)] CH3COOH (aq) + CH3OH (aq)}\]

Why is it important to have clean surface in surface studies?

Why is chemisorption referred to as activated adsorption?

Why do physisorption and chemisorption behave differently with rise in temperature?

What is the role of activated charcoal in gas mask used in coal mines?

Give an example where physisorption changes to chemisorption with rise in temperature. Explain the reason for change.

What is the role of diffusion in heterogenous catalysis?

Assertion: Detergents with low CMC are more economical to use.

Reason: Cleansing action of detergents involves the formation of micelles. These are formed when the concentration of detergents becomes equal to CMC.

What is the role of adsorption in heterogenous catalysis?

Which of the following elements can be involved in pπ – dπ bonding?

On heating lead nitrate forms oxides of nitrogen and lead. The oxides formed are ______.

Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.