Question

X is an element with atomic number 20.(1) is it a metal or non-metal?(2)which of the two x or mg with atomic number 12 is more reactive? (3) what is the valency of x

Answer 1

(1) Atomic number of X is 20. Electronic configuration is 2, 8, 8, 2. Valence electrons in X is 2. Metals have valence electrons less than 4. So X is metal.
(2) Atomic number of Mg is 12. Electronic configuration is 2, 8, 2. Atomic number of Mg is less than X. It means Mg will come before X. They will lie in same group as both have same number of valence electrons. Reactivity of metals increases down the group. I means X is more reactive than Mg.
(3) Valency of X is 2 as it has two electrons in its valence shell. After losing two electrons it will achieve noble gas configuration. Thus it has valency 2.