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. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

Give examples of non-conductors and conductors.

Write the activity to make simple electroscope.

The minimum charge on an object is

Five balls numbered $1$ to $5$ are suspended using separate threads. Pairs $(1, 2)$, $(2, 4)$ and $(4, 1)$ show electrostatic attraction, while pair $(2, 3)$ and $(4, 5)$ show repulsion. Therefore ball $1$ must be