Question

Among $C{{H}_{4}}$, $N{{H}_{3}}$ and ${{H}_{2}}O$, acidity of ${{H}_{2}}O$ is maximum because:
A.Oxygen contains two lone pair of electron
B.Bond angle in ${{H}_{2}}O$ is less than $128{}^\circ 28$
C.Oxygen is more electronegative than $N$ or $C$
D.${{H}_{2}}O$ is an associated liquid

Answer 1

Methane is a neutral molecule, whereas ammonia is a basic molecule having much higher pH value.
-The three molecules given in the question have a common atom hydrogen, so we will do a comparative study by considering the different atoms.

Complete answer:
-Acidity of a compound or an ion or a molecule is the ability of that molecule to release its proton or the ability to accept lone pairs of electrons. Bronsted bases on the other hand, are the bases which can accept protons from a molecule. For example ammonia can accept one proton to form ammonium ion. Similarly, water can accept a proton in order to form hydronium ions. Whereas, bronsted acids are those which releases protons from a molecule, to the acceptor molecule or ion. Example of bronsted acid could be hydrochloric acid, which is a strong acid so it readily releases its proton in the solution.
-In the given question ammonia is basic in nature as it can readily accept protons or donate a lone pair of electrons in order to complete its octet. On the other hand methane is a neutral molecule as all the four hydrogens are tightly bound to the carbon atom, so none of the hydrogens are going anywhere.
-Therefore it has a pH $7$. Now if we look at the water molecule, it can easily release a proton in order to form hydroxyl ions. Among the three given molecules, there is a difference of one atom, the second type of atom is hydrogen in all of them. So we could have a comparative analysis of three of them on the basis of electronegativity.
-Electronegativity can be defined as a measure of the tendency of an atom to attract the shared pair of electrons involved in the bonding. We all know that oxygen has a comparatively higher electronegativity value than nitrogen and carbon. Hence, it will attract the electrons of the two hydrogen attached to it in the structure of the water molecule.
Hence, Option C is correct.

Note:
-The pH of the solution can give us a fair idea about the concentration of hydronium ion and hydroxyl ions in a molecule.
-The pH and pOH of a water solution at $25{}^\circ C$ are related by the following equation.
$pH\text{ }+\text{ }pOH\text{ }=\text{ }14$
-The acidity of a molecule or ion is determined by the ability of it to accept lone pairs of electrons. The more easily they accept the electrons, the more acidic they will be.