Question

The most active metal is:
(A) Be
(B) Ca
(C) Ba
(D) Mg

Answer 1

Hint: The elements which can react by donating, accepting or sharing electrons are known as active elements. In order to solve this question, we need to know the reactivity of metals. Mostly s-block elements are reactive and reactivity increases down the group.

Complete answer:
Beryllium: Beryllium is a chemical compound of group two which is donated by symbol Be. Atomic number of beryllium is four. It is a rare element in the universe. Beryllium is a free element; it is a steel-grey, strong, lightweight and a brittle alkaline earth metal.
Calcium: It is a chemical element of group two and it is denoted by symbol Ca. Atomic number of calcium is 20. Calcium is an alkaline earth metal that forms a dark oxide-nitride layer when exposed to air. It is the fifth most abundant element in earth's crust.
Barium: Barium is a chemical element with the symbol Ba and atomic number 56. It is a group of two elements. Barium is soft, silvery and alkaline earth metal.
Magnesium: Magnesium is a chemical element of group two and it is denoted by symbol Mg. Atomic number of magnesium is twelve. Magnesium is a shiny gray solid with close resemblance to other five elements of the same group.
The atomic size increases down the group. Hence the number of shells increases down the group and so the difference between the valence electrons and the nucleus increases. That is why, ionisation energy decreases down the group as less energy will be needed to remove an electron for reaction.
Among Be, Mg, Ca and Ba, the barium is located lowest in the group 2. Therefore, barium will be the most active metal because its ionisation energy is lowest and it will react easily.
The correct answer is option C.

Note:
Ionisation energy is the energy needed to remove a valence electron from the outermost shell of an atom. The outermost electrons which are ready to take part in a reaction are known as valence electrons.