Question

Assertion: ${{H}_{2}}O$ is the only hydride of group-16 which is liquid at ordinary temperature.
Reason: In ice, each oxygen atom is surrounded by two covalent bonds and two hydrogen bonding.
A. Both Assertion and Reason is correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

Hint: To solve this question discuss each of the assertions and reasons one by one. Water is liquid at ordinary temperature or room temperature due to the extensive hydrogen bonding of water and therefore it has high boiling point.

Complete answer:
Let us discuss Assertion and Reason one by one,
A) ${{H}_{2}}O$ is the only hydride of group-16 which is liquid at ordinary temperature.
As we know that the group-16 of the periodic table belongs to the oxygen family which is also called as chalcogens. The elements that are present in the group 16 are oxygen, sulphur, selenium, tellurium and polonium. These elements can be found in both combined and free states in nature.
Some of the elements of group 16 forms the hydride and hydride of oxygen and hydride of sulphur are most common among them. Hydride of oxygen is responsible for the formation of water ${{H}_{2}}O$. As we know that the electronegativity of oxygen is very high, so it has the ability to form the hydrogen bonds and thus they form the water molecules which are liquid at the ordinary temp because in the water molecules there are extensive hydrogen bonding and because of it exist as an associated molecule. Due to extensive hydrogen bonding the boiling point increases upto 373 k at the standard pressure and hence it exists as liquid at the ordinary temperature. Therefore we can say that the Assertion is correct.
B) In ice, each oxygen atom is surrounded by two covalent bond and two hydrogen bonding
As we know that in ice each of the oxygen atoms is surrounded by the four hydrogen atoms in such a way that the two of the four hydrogen atoms are linked by hydrogen bonds and the other two hydrogen bonds are linked through an oxygen bond by the covalent bonds. Water molecules in the ice (solid state) are associated with the four other water molecules by hydrogen bonding in the tetrahedral manner. And this gives rise to the open cage like structure that prevents the close packing of the molecule. Therefore we can say that the Reason is also correct. But the Assertion and Reason are not interrelated. Therefore both the Assertion and Reason are correct but reason is not the correct explanation for Assertion.

Thus the correct option will be (B).

Note: When water molecules are present in the liquid state then they are held through the intermolecular hydrogen bonding. Each of the oxygen tends to form two hydrogen bonds with the help of its two lone pairs of electrons. The density of water molecules in liquid state is more than the ice. Hydrogen sulphide exists as a gas at the ordinary temperature due to less electronegativity and absence of hydrogen bonding.