Which atom is the largest
K
K+
Ca
Ca2+
Li

Explanation:

K: 2, 8, 8, 1 but 19p+

K+: 2, 8, 8 but 19p+

Ca: 2, 8, 8, 2 but 20p+

Ca2+, 2, 8, 8 but 20p+

K and Ca are larger than their corresponding ions because of one more energy level, so Li is the smallest.

K and Ca have the same no. of electron shells but K has less p+ than Ca. so the attraction between electron and p+ in K is less than that in Ca. Therefore, K is larger than Ca.

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).