An element consists of a mixture of three isotopes $A$, $B$, and $C$ of masses $m_1$, $m_2$, and $m_3$ respectively. If the relative abundances of the three isotopes $A$, $B$, and $C$ are in the ratio $2:3:5$, the average mass of the element is:

Particles and their anti-particles have

Give one example each of central force and non-central force.

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.

Read the following statements:
$(A)$ Volume of the nucleus is directly proportional to the mass number.
$(B)$ Volume of the nucleus is independent of mass number.
$(C)$ Density of the nucleus is directly proportional to the mass number.
$(D)$ Density of the nucleus is directly proportional to the cube root of the mass number.
$(E)$ Density of the nucleus is independent of the mass number.
Choose the correct option from the following options.

In the nuclear reaction ${ }_{7}^{14} N + X \rightarrow { }_{6}^{14} C + { }_{1}^{1} H$, the $X$ will be