The atomic weight of boron is $10.81$ and it has two isotopes $_5B^{10}$ and $_5B^{11}$. The ratio of $_5B^{10} : _5B^{11}$ in nature is:

Given below are two statements $:$ one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A) :$ The density of the copper $\left({ }_{29}^{64} Cu \right)$ nucleus is greater than that of the carbon $\left({ }_6^{12} C \right)$ nucleus.
Reason $(R) :$ The nucleus of mass number $A$ has a radius proportional to $A^{1/3}$.
In the light of the above statements,choose the most appropriate answer from the options given below.

Which of the following is not made by quarks?

The most stable particle in the Baryon group is

Which of the following pairs of nuclei are isobars?

Estimate the approximate volume of an aluminium nucleus $(A=27)$.
$\text{Use } (R_0 \simeq 1.0 \times 10^{-15} \ m, \pi \simeq 3)$.