The electronic configuration of metal ‘A’ is 2,8,1 and that of metal ‘B’ is 2,8,2. Which of the two metals is more reactive? Write their reaction with dilute hydrochloric acid.

While moving from left to right in a periodic table, the chemical reactivity of the elements decreases from sodium to silicon and then it increases from phosphorus to chlorine. Electronic configuration of metal A is given as 2,8,1, (same as the electronic configuration for sodium metal) while that of metal B is 2,8,2 (the electronic configuration of magnesium metal). Meanwhile, the first element of the third period, sodium has 1 valence electron, which it can lose easily to react with other substances. For this reason, sodium is a highly reactive metal. The second element, magnesium has 2 valence electrons, which is not so easy to lose. For this reason, magnesium is less reactive than sodium.

Reactions with dilute hydrochloric acid:

Na + HCl → NaCl + H₂

Mg + HCl → MgCl₂ + H₂