Identify, the elements with the following property and arrange them in increasing order of their reactivity.
(a) An element which is a solt and reactive metal.
(b) The metal which is an important constituent of limestone
(c) The metal which exists in liquid state at room temperature.

Explanation

(a) An element which is soft and reactive metal sodium (Na) potassium (K) as alkali metals are soft and reactive
(b) Limestone is calcium carbonate `CaCO_(3)`. The important constituent of limestone is calcium (Ca)
(c) Metal which exists in liquid state at room temperature is mercury (Hg) So, the increasing order of their reactivity
Mercury `lt` Calcium `lt` Sodium
or Hg `lt` Ca `lt` Na.