21. It is now believed that protons and neutrons are themselves built out of more elementary particles called quarks. A proton and a neutron consists of three quarks each. Two types of quarks, the so called 2 up quark (denoted by u) of charge +e and the down 3 quark (denoted by d) of charge e, together with 3 electrons build up ordinary matter. Suggest a possible quark composition of a proton and neutron. (NCERT) 22. Two identical point charges, q each, are kept 2 m apart in air. A third point charge Q of unknown magnitude and sign is placed on the line joining the charges such that system remains in equilibrium. Find the position and nature of Q. (CBSE 2019)