Consider the following elements :
Na, Ca, Al, K, Mg, Li
(a) Which of these elements belong to the same period of the periodic table?
(b) Which of these elements belong to the same group of the periodic table?
(a) Sodium (Na), magnesium (Mg) and aluminium (Al) belong to the same(third) period of the periodic table.
(b) Lithium (Li), sodium (Na) and potassium (K) belong to the same group(group 1) of the periodic table.