According to the general trend the atomic radius for a periodic of elements (increases/decreases) proceeding from left to right in the periodic table

Going from left to right across a period, atomic radius decreases. although you are adding more electrons, the electrons are losing the tug of war with the protons.

the child will have heterozygous dominant chromosomes as characters of his father are dominant over the characters of his mother.

the child is heterozygous

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.