Which of the following is the most powerful reducing agent in the gas phase ?

Options

A. Cs
B. Li
C. K
D. Na

Answer

A

Explanation

The tendency of an element to lose electrons in the gas phase is measured in terms of ionization enthalpy. Lower the `Delta_(i)H`, greater the tendency to lose electrons, stronger the reducing character, and higher the reactivity of the element. Since `Delta_(i)H` decreases down the group, reducing character (or reactivity in the gas phase) increases from Li to Cs : `Li lt Na lt K lt Rb lt Cs`.