Directions: The answer to the following question is a single digit integer ranging from 0 to 9. Enter the correct digit in the box given below.
How many open chain structures are possible for N-Methly butanamine (including it) that are referred to as metamers.


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: $g = 10\,\text{m s}^{-2}$) 
Method used for separation of mixture of products (B and C) obtained in the following reaction is: 