Question

Oxygen gas is ______ in weight compared to water.
(A) Lighter
(B) Heavier
(C) Equal
(D) None of these

Answer 1

Hint :For this question, we need to compare physical and chemical properties of oxygen and water at room temperature. We must also know that the weight of a compound is equal to the density of the compound at unit volume.

Complete Step By Step Answer:
We know that, at room temperature the water is present at its liquid state whereas the oxygen gas is present at its gaseous state and on the basis of the fact that gases are less dense than the fluids, we can conclude that water is denser than oxygen gas at room temperature.
Also, we know that water is a polar compound because the structure of the water molecule is not symmetrical and there is an appreciable difference between the electronegativities of hydrogen and oxygen atoms which makes it a polar molecule. Now, due to this polarity the force of attraction between the ions in the water molecule increases pulling the molecules to become denser.
Whereas oxygen gas is a nonpolar gas that allows it to float in the atmosphere and the remains as separate molecules. Hence from the above conclusions we can say that oxygen gas is lighter in weight as compared to water.
Thus, option (A) is the correct answer.

Note :
We can also use the concept of hydrogen bonding to explain the denser property of water than air. Although the atomic mass of oxygen molecules is more than the atomic mass of water molecules these can be compared only if the two molecules are existing in the same phase.