Question

Consider $ {\text{Mg}}{\left( {{\text{HC}}{{\text{O}}_{\text{3}}}} \right)_{\text{2}}} $ and choose the correct option.
(A) Oxidation state of hydrogen is $ + 5 $ .
(B) Oxidation state of carbon is $ + 1 $ .
(C) Oxidation state of hydrogen is $ + 1 $
(D) Oxidation state of hydrogen is $ + 4 $
(E) None of the above.

Answer 1

Hint: The oxidation state of any element is defined as the combining capacity of the element in a particular compound and it describes the number of electrons that the element may gain or have lost to form that compound.

Complete step by step solution:
The oxidation state of an element is determined as follows:
Consider that the oxidation state of hydrogen in magnesium carbonate is “x”. The oxidation states of magnesium here is $ + 2 $ which is its valency as well and it is fixed, carbon has an oxidation state $ + 4 $ which is also its valency, the oxygen atom has and oxidation state $ \left( { - 2} \right) $ which is also its valency. Therefore the oxidation state of hydrogen here is:
 $ 2 + 2\left( {{\text{x}} + 2 + \left( { - 2 \times 3} \right)} \right) = 0 $
Or, $ 2 + 2{\text{x + 8 - 12}} = 0 $
Or, $ 2{\text{x = 2}} $ and,
 $ {\text{x = 1}} $ .
Therefore the oxidation state of hydrogen in the compound is ( $ + 1 $ ) and the correct option is C.

Note:
The difference between the oxidation state and the valence of the element is that the oxidation state of the element can be fractional as well as negative numbers but the valence of the element can be only a number without any positive or negative sign.
An example of the same will be that oxygen is its neutral or free state has oxidation number zero, while in the peroxides the oxidation number is $ \left( { - 1} \right) $ , in water and other oxides the oxidation number is $ \left( { - 2} \right) $ while in fluorine oxide the oxidation number of oxygen is ( $ + 1 $ ).