Question

Which of the following statements regarding the periodic trends of chemical reactivity of the alkali metals and the halogens is correct?

• A. The reactivity decreases in the alkali metals but increases in the halogens with increase in atomic number
• B. In alkali metals the reactivity increases but in the halogens it decreases with increase in atomic number down the group.
• C. Chemical reactivity increases with increase in atomic number down the group in both the alkali metals and halogens.
• D. In both the alkali metals and the halogens, the chemical reactivity decreases with increase in atomic number down the group.

Answer 1

The correct option is B

In alkali metals the reactivity increases but in the halogens it decreases with increase in atomic number down the group.

In alkali metals, the reactivity increases down the group due to a decrease in first ionization enthalpy.
But in the case of halogens, the reactivity decreases down the group due to a decrease in their electron gain enthalpy.