Question

Which among the following hydrides is NOT a reducing agent?
A. ${H_2}O$
B. ${H_2}S$
C. ${H_2}Te$
D. ${H_2}Se$

Answer 1

In a redox reaction, we have oxidizing as well as reducing agent. Reducing agent facilitates the reduction by getting oxidized. Similarly, the oxidizing agent tends to get reduced thereby facilitating the oxidation of other species.

Complete step by step answer:
The periodic classification of elements can help us in deducing various trends and properties of elements depending upon their position in the periodic table. Let’s use these trends and the properties to deduce the reducing property of elements.
In the periodic table, size of the element increases down a group. Due to this the bond length for the same category of compounds also increases because as the size increases, the atoms are separated by a longer distance. As we know that the bond strength is inversely proportional to the bond length. So, we can say that the bond dissociation energies for a given category of compounds of the elements belonging to the same group decrease down the group.
We can define the reduction and oxidation in terms of removal or addition of hydrogen atoms as well. The removal of hydrogen is considered to be oxidation whereas addition of hydrogen is considered to be reduction.
We can use the above discussed trend in the bond dissociation energies for a given category of compounds of the elements belonging to the same group to deduce the trend in the removal of hydrogen as well. As it has been established that the bond dissociation energies for a given category of compounds of the elements belonging to the same group decrease down the group, it can be inferred that removal of hydrogen becomes easier or the acidic nature gets increased down a group. So, it would be easier to remove hydrogen from the last element in a group.
As we know that oxidizing agents tend to get reduced whereas reducing agents prefer to get oxidized. Using the previous discussion, we can say in a group, the reducing property increases down the group.
From the periodic classification of elements, we know that oxygen, sulfur, tellurium and selenium belong to the group $16$ of the periodic table. We can deduce that it is the hydride of tellurium which is the strongest reducing agent. On the similar lines, it can be inferred that the hydride of oxygen (water) does not act as a reducing agent. Electronegativity of oxygen also makes it least probable to any increase in its oxidation number.

Hence, the correct option is A.

Note:
We have to be careful with the use of reducing agents and oxidizing agents as it can be quite confusing at times. Oxidation is defined as loss of electrons while reduction is defined as gain of electrons.