The weight of one molecule of CaCO₃ is 2. The gaseous hydrocarbon having formula CnH₂n+2 diffuses twice as quickly as sulphur dioxide. The molecular formula of hydrocarbon is

Molar mass of $\text{CaCO}_3 = \text{Ca} + \text{C} + 3 \times \text{O}$
Molar mass of $\text{CaCO}_3 = 40.08 + 12.01 + 3(16.00) = 40.08 + 12.01 + 48.00 = 100.09 \text{ g/mol}$

Weight of one molecule $= \frac{\text{Molar mass}}{\text{Avogadro's number}}$
Weight of one molecule $= \frac{100.09 \text{ g/mol}}{6.022 \times 10^{23} \text{ molecules/mol}}$
Weight of one molecule $\approx 1.66 \times 10^{-22} \text{ g}$

The correct option is b) $\boxed{1.66 \times 10^{-22} \text{ gm}}$.

2. The gaseous hydrocarbon having formula CnH₂n+2 diffuses twice as quickly as sulphur dioxide. The molecular formula of hydrocarbon is

Graham's Law states that the ratio of the rates of diffusion of two gases is inversely proportional to the square root of the ratio of their molar masses:

Let the hydrocarbon be gas 1 and sulphur dioxide ($\text{SO}_2$) be gas 2.
Given: $\text{Rate}_{\text{hydrocarbon}} = 2 \times \text{Rate}_{\text{SO}_2}$, so $\frac{\text{Rate}_{\text{hydrocarbon}}}{\text{Rate}_{\text{SO}_2}} = 2$.
Molar mass of $\text{SO}_2 = 32.07 (\text{S}) + 2 \times 16.00 (\text{O}) = 64.07 \text{ g/mol}$.

Squaring both sides:

The hydrocarbon has the formula $\text{C}_n\text{H}_{2n+2}$.
Molar mass of $\text{C}_n\text{H}_{2n+2} = n(12.01) + (2n+2)(1.01) = 12.01n + 2.02n + 2.02 = 14.03n + 2.02$.
Set this equal to the calculated molar mass:

For $n=1$, the formula is $\text{C}_1\text{H}_{2(1)+2} = \text{CH}_4$.
The molar mass of $\text{CH}_4 = 12.01 + 4(1.01) = 16.05 \text{ g/mol}$, which matches our calculation.

The correct option is d) $\boxed{\text{CH}_4}$.

3. The structure of NaCl is

The correct option is b) $\boxed{\text{Face centered cubic lattice}}$.

4. Paste of lime in water is called

The correct option is c) $\boxed{\text{milk of lime}}$.

5. Which one of the following elements is macro element?

The correct option is a) $\boxed{\text{Mg}}$.

6. Which one of the following is amphoteric oxide?

The correct option is b) $\boxed{\text{ZnO}}$.

7. The formula of ammonium carbamate formed during manufacture of urea is

The correct option is b) $\boxed{\text{NH}_2\text{COONH}_4}$.

8. Hydrometallurgy is applied for the reduction of

The correct option is c) $\boxed{\text{Ag}_2\text{S}}$.

9. White phosphorous reacts with caustic alkali to give

The correct option is **c)