How are \({ d }_{ xy }\ \)and   \(d{ x }^{ 2 }-{ y }^{ 2 }\) orbitals related?

1

(a)

The \({ d }_{ xy }\) orbital is exactly like  \(d{ x }^{ 2 }-{ y }^{ 2 }\) orbital except that its lobes are at an angle of \(45^{0}\)to the lobes of \(d{ x }^{ 2 }-{ y }^{ 2 }\)orbital.

Why is NaCl harder than sodium metal?

1

(a)

This is because in NaCl, there is strong ionic bond between Na⁺ and Cl^-1 whereas in Na metal, there is weak metallic bond.

The experimentally determined N-F bond length in NF₃ is greater than the sum of the single covalent radii of n and F.

1

(a)

This is because both N and F are small and hence, have high electron density. So, they repel the bond pairs thereby making the N-F bond length larger.

Why are the gases helium and hydrogen not liquefied at room temperature by applying very high pressure?

1

(a)

Because their critical temperature is lower than room temperature. (Gases cannot be liquefied above the critical temperature by applying even very high pressure.)

Under what condition, the heat evolved or absorbed in a reaction is equal to its free energy change?

1

(a)

As \(\Delta G=\Delta H-T\Delta S\). Thus, \(\Delta G=\Delta H\) only when either the reaction is carried out at 0K or the reaction is not accompanied by any entropy change, i.e. \(\Delta S\) = 0.

Ice melts slowly at higher altitudes. Explain why?

1

(a)

Ice(s) ⟶ Water
The melting of ice is favoured at high pressure because there is decrease in volume in the forward reaction. Since at high altitudes, atmospheric pressure is low and therefore, ice melts slowly.

Can we use KCI as electrolyte in the salt bridge of the cell, Cu(s) I Cu² (aq) II Ag⁺(aq) I Ag(s)?

1

(a)

KCI cannot be used as electrolyte in the salt bridge because CI^- ions will combine with Ag⁺ ions to form white precipitates of AgCI

Why is dihydrogen not preferred in balloons these days?

1

(a)

Dihydrogen is highly combustible and hence, is likely to catch fire in the presence of excess of air. That's why it is not preferred in balloons now a days.

Will CCI₄ give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.

1

(a)

CCI₄ will not give a white ppt of AgCI with AgNO₃ solution because CCI₄ is a covalent compound. It does not ionise to give CI^- ions required for the formation of AgCI precipate.

Ozone is a gas heavier than air. Why does ozone not settle down near the earth?

1

(a)

Ozone is thermodynamically unstable and decomposes back to molecular oxygen before reaching near the earth surface. Moreover, as negligible amount of UV-rays reach near the surface hence formation of ozone near the surface is rare.