The correct answer is (B): Both (A) and (R) are true but (R) is not the correct explanation of (A).
The outer most shell of Boron is 2 and its maximum covalency is 4.
Therefore, boron cannot form BF63-.
Hence Assertion is correct.
Boron is the first element of group-13 of modern periodic table. It is very small in size.
But it does not provide correct explanation of Assertion.
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: $g = 10\,\text{m s}^{-2}$) 