Question

Which of the following is the most reactive non-metal?
(a). Chlorine
(b). Hydrogen
(c). Fluorine
(d). Selenium

Answer 1

Hint: Reactivity of non-metals depends on its tendency to obtain its nearest noble gas configuration. The element which fills its octet easily is the most reactive. Since all elements given to us are non-metals, compare them on the basis of their individual electronegativities.

Complete step-by-step solution -

Non-metals are p-block (group 13-17) elements (exception – Hydrogen is placed in s block). Non-metallic elements usually have 4-7 elements in its outermost shell.
Non-metals have a tendency to gain electrons to complete its octet (duet – in case of Hydrogen). Non-metals with an electronic configuration closest to its stable electronic configuration are the most reactive. This is because it will react quickly to reach a stable octet.

Reactivity of any non-metal is decided by the following factors –
Electronegativity (high)
Electron Affinity (high)
Ionisation Potential (high)
Amongst these, electronegativity is the most widely used parameter.
The order of increasing electronegativity for the given metals is –
$H\text{ }\left( 2.2 \right)\text{ } < \text{ }Se\text{ }\left( 2.55 \right)\text{ } < \text{ }Cl\text{ }\left( 3.16 \right)\text{ } < F\text{ }\left( 3.98 \right)$
Amongst the given non-metals, Fluorine has the maximum electronegativity (3.98).
Owing to the higher electronegativity, smaller size, we can say that the tendency of fluorine to complete its octet is highest.
Therefore, the answer is option (c), fluorine.

Additional information:
From this, we can say that reactivity of non-metals in groups increases from left to right. Also, reactivity of non-metals decreases as we go down the group.

Note: Metals on the other hand tend to achieve its nearest noble gas configuration by losing electrons. Therefore, metals have a low electronegativity, low electron affinity and low ionisation potential.