Question

The compound having only primary hydrogen atom is:
A.Butane.
B.Isobutene.
C.Cyclohexane.
D.\[2,3-dimethyl-but-2-ene.\]

Answer 1

Hint: We know what primary hydrogen is. The hydrogen attached with primary carbon is known as primary hydrogen. We will draw the geometry of all the given molecules then we will find the primary carbon to determine the compound having all primary hydrogen atoms.

Complete answer:
In order to solve the given problem, first we will understand the concept behind the existence of different structures of organic compounds with the same chemical formula. Further we will understand the meaning of primary and secondary atoms in a compound and finally on the basis of structure of the organic compounds given in the options we will find the correct answer.
A carbon atom has four valances. Primary carbon is the carbon which is attached with one other carbon; only other three valences are satisfied by hydrogen atoms. $-C{{H}_{2}}-C{{H}_{3}}$ here \[C{{H}_{3}}\] is the primary hydrogen atom. The carbon attached with three other carbons is known as tertiary carbon and the hydrogen atoms attached with tertiary carbon are known as tertiary hydrogen atoms. Here, except cyclohexane, all have primary carbon and primary hydrogen but only isobutene has all primary hydrogen.
The compound having only the primary hydrogen atom is cyclohexane. Carbon atoms are attached to two Carbon atoms and two Hydrogen atoms. Such Carbon atoms are called primary Carbon atoms and Hydrogen atoms are called primary Hydrogen atoms.
Therefore, the correct answer is option B.

Note:
Remember that the carbon attached with two other carbon is known as secondary carbon and the hydrogen atoms attached with secondary carbon are known as secondary hydrogen atoms. Isobutene has tertiary carbon but not tertiary hydrogen.