Question

It is now known that a proton and a neutron consist of three elementary units called 'quarks'. Two types of quarks are involved the 'up' quark (u) of charge $+\frac{2}{3}e$ and the 'down' quark (d) of charge $-\frac{1}{3}e$, where e is the magnitude of electron's charge. $\overline{u}$ and $\overline{d}$ are their antiparticles. An antiparticles has the same magnitude of charge as the particle but of opposite sign. The possible compositions of a proton and a neutron are

• A. $p:uud;n:udd$
• B. $p:uuu;n:ddd$
• C. $p:uu\overline{d};n:ud\overline{d}$
• D. $p:uu\overline{u};n:ud\overline{d}$

Answer 1

The correct option is A $p:uud;n:udd$

$\begin{array}{c}\text{The net charge on proton is +ve. This can be}\\ \text{obtained by p}=(\frac{2}{3}+\frac{2}{3}-\frac{1}{3})e=+e\end{array}$

$\begin{array}{c}\text{hence, proton has two 'up' quarks and a 'down'}\\ \text{quark.}\end{array}$

$\begin{array}{c}\text{The net charge on neuon is}0.\text{This can be}\\ \text{obtained by}n=(\frac{2}{3}-\frac{1}{3}-\frac{1}{3})e=0\end{array}$

$\begin{array}{c}\text{hence, neutron has one "up' quark and two}\\ \text{'down' quark}\\ \text{p:uud \&}n\text{: udd hence option A is correct}\end{array}$