Calcium is an element with atomic number $20$.
$(i)$ Will it be a metal or a non-metal?
$(ii)$ What will be its valency?
$(iii)$ What would be the formula of its chloride?
$(iv)$ Will it be larger or smaller than $K$ (Potassium)?

(A-D) $(i)$ Calcium $(Ca)$ has an electronic configuration of $2, 8, 8, 2$. Since it has $2$ valence electrons,it tends to lose them to achieve a stable octet,making it a metal.
$(ii)$ The valency of an element is determined by the number of electrons it needs to lose or gain to complete its octet. Since Calcium loses $2$ electrons,its valency is $2$.
$(iii)$ The valency of Calcium $(Ca)$ is $+2$ and the valency of Chlorine $(Cl)$ is $-1$. By criss-crossing the valencies,the formula of its chloride is $CaCl_{2}$.
$(iv)$ Calcium $(Ca)$ is smaller than Potassium $(K)$. As we move from left to right across a period,the atomic radius decreases because the nuclear charge increases,pulling the electrons closer to the nucleus.