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

Pick out the correct statement from the following.

The radius of a nucleus with mass number $27$ is $R$. Which of the following is true about a nucleus whose radius is $2R$?

The radius $R$ of a nucleus of mass number $A$ can be estimated by the formula $R = (1.3 \times 10^{-15}) A^{1/3} \; m$. It follows that the mass density of a nucleus is of the order of $(M_{\text{prot}} \cong M_{\text{neut}} = 1.67 \times 10^{-27} \; kg)$.

The radius of ${ }_{29} Cu^{64}$ nucleus in Fermi is (given $R_{0}=1.2 \times 10^{-15} \ m$)

It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. $A$ proton and a neutron consist of three quarks each. Two types of quarks,the so-called 'up' quark (denoted by $u$) of charge $+(2/3)e$,and the 'down' quark (denoted by $d$) of charge $-(1/3)e$ together with electrons build up ordinary matter. Suggest a possible quark composition of a proton and neutron.