Question

Statement $1$: correct order of acidic strength is $C{H_3}C{H_3} > C{H_2} = C{H_2} > HC = CH$.
Statement $2$: $C - H$ bond energy in ethene is more than ethane but less than ethyne.
(A) Statement $1$ is true, statement $2$ is true and statement $2$ is the correct explanation for statement $1$.
(B) Statement $1$ is true, statement $2$ is true and statement $2$ is NOT the correct explanation for statement $1$.
(C) Statement $1$ is true, statement $2$ is false.
(D) Statement $1$ is false, statement $2$ is true.

Answer 1

Hint : In this question, we need to check the hydrogen atom or proton donating nature of hydrocarbons. The proton donating nature depends upon the $s -$character of the carbon atom to which the donating hydrogen atom is attached and is called acidity of hydrocarbons or bond energy of hydrocarbons. More the $s -$character, more is the electronegativity of carbon and more will be the acidity or the bond energy.

Complete Step By Step Answer:
Hydrocarbons have a tendency of donating hydrogen atoms. The electronegative carbon creates a high positive charge on the hydrogen atoms on donating and thus the hydrocarbons becomes acidic in nature and therefore, hydrocarbons are referred to as proton donors.
In ethyne, there is a presence of acidic hydrogen which has $50\%$ $s -$character. Here, both the hydrogen atoms are identical and connected with carbon which is $sp -$ hybridised. Hence, Ethyne is most acidic.
In ethene, the hydrogen atom is attached to a $s{p^2} -$hybridized carbon atom. Here, the $s -$character is around $33.33\%$ and four identical hydrogen atoms are connected to the carbon atom. Therefore, ethene is less acidic than ethyne.
In ethane, the hydrogen atom is attached to a $s{p^3} -$hybridized carbon atom. Here, the $s -$character is $25\%$ and six identical hydrogen atoms are connected to the carbon atom. Therefore, ethane is least acidic among all three.
This means that statement $1$ is false and statement $2$ is true.
Hence, the correct option is D.

Note :
In the solution above, hydrogen atoms are referred to as being identical. The term ‘identical’ is used to describe the bond nature (triple bond, double bond or single bond) of hydrogen atoms as well as whether they contain any kind of charge on them as all of them need to be the same. Hence, students shouldn’t get themselves confused by thinking in terms of atomic radii or atomic size etc. For a quick reference, the $s-$ character can be easily calculated by simply dividing $1$ by the number of $p-$orbitals present in hybridization of hydrocarbons. Here, $1$ is used to denote the $s-$orbital.