There are four isomer possibilities for the molecular formula C4H10O, but only one of them is chiral in nature. A chiral molecule is one that is not superimposable on its mirror image. In other words, it has a non-superimposable mirror image, just like our hands. Let's analyze each isomer to determine which one is chiral.

1. n-Butanol: n-Butanol is the simplest isomer with the molecular formula C4H10O. It is also known as 1-butanol. This molecule has a linear structure with a hydroxyl group (-OH) attached to the first carbon atom. It is not chiral because it has a plane of symmetry, which means its mirror image can be superimposed on the original molecule.

2. Isobutanol: Isobutanol is an isomer of butanol with the same molecular formula but a different structure. It is also known as 2-methyl-1-propanol. This molecule has a branched structure with a methyl group (-CH3) attached to the second carbon atom. It is not chiral because it has a plane of symmetry, just like n-butanol.

3. Secondary butanol: Secondary butanol is another isomer of butanol with the molecular formula C4H10O. It is also known as 2-butanol. This molecule has a branched structure with a hydroxyl group (-OH) attached to the second carbon atom. It is chiral because it does not have a plane of symmetry. Its mirror image cannot be superimposed on the original molecule.

4. Tertiary butanol: Tertiary butanol is the final isomer of butanol with the molecular formula C4H10O. It is also known as 2-methyl-2-propanol. This molecule has a branched structure with a methyl group (-CH3) attached to the second carbon atom. It is not chiral because it has a plane of symmetry.

Therefore, out of the four isomers of C4H10O, only secondary butanol (2-butanol) is chiral in nature. Hence, the correct answer is option B) 1.