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') and 'down' quark ( denoted by 'd') of charge `(2)/(3) e ` and `(-1)/(3) e` respectively , together with electrons build up ordinary matter. Suggest a possible quark composition of a proton and a neutron.

Explanation

The charge of a proton `+e `.
A proton can be made up of 2u's and 1d because in that case the total charge `= ( 2e)/( 3) + ( 2e)/( 3) - ( e )/( 3) = e `
`:.` A proton can be composed as uud.
A neutron has no charge. It can be made up of 2d's and 1u because in that case the total charge ` `( 2)/( 3) e - (1)/( 3) e - (1)/( 3) e = 0`
`:.` A neutron can be composed as udd.