| Column-I | Column-II | ||
| P | N2O5 | (i) | N–N bond |
| Q | N2O | (ii) | N–O–N bond |
| R | N2O4 | (iii) | N=N / N≡N bond |
| S | NO2 | (iv) | N=O bond |
P – (ii), Q – (iii), R – (i), S – (iv)
Method used for separation of mixture of products (B and C) obtained in the following reaction is: 
In the given figure, the blocks $A$, $B$ and $C$ weigh $4\,\text{kg}$, $6\,\text{kg}$ and $8\,\text{kg}$ respectively. The coefficient of sliding friction between any two surfaces is $0.5$. The force $\vec{F}$ required to slide the block $C$ with constant speed is ___ N.
(Given: $g = 10\,\text{m s}^{-2}$) 