Question

Identify the incorrect statement.

[1 mark]

• A. The oxidation state and valency can be the same for an element.
• B. Oxidation state of nitrogen in ${NH}_3$ is -3.
• C. Oxidation state of oxygen in $H_{2}O$ is +2.
• D. The valency of elements first increases, and then decreases on going from left to right across a period.

Answer 1

The correct option is C Oxidation state of oxygen in $H_{2}O$ is +2.

There are numerous cases where the oxidation state and valency are the same for an element.

Example: H has a valency of 1 and its oxidation state is also +1 in $H^{+}$.
The oxidation state of N in ${NH}_3$ is -3 while the oxidation state of O in $H_{2}O$ is -2.

Valency is the number of electrons required by an element to complete its octet. So, while going from left to right across a period, the valency first increases and then decreases.
For example, the valency of group 1, group 14, and group 17 elements is 1, 4, and 1, respectively.