Question

When cyclohexane is poured in water, it floats because:-
(a) cyclohexane is in boat form
(b) cyclohexane is less dense than water
(c) cyclohexane is in chair form
(d) cyclohexane is in crown form

Answer 1

Cyclohexane, a multiplanar ring has two conformations; the chair and the boat conformation. Density of cyclohexane is less than water and the substance having lesser density, is always lighter than the other and thus, the lighter one floats. Now you can easily answer the given statement accordingly.

Complete answer:
First of all , let’s discuss cyclohexane. Cyclohexane is a multi planar or puckered ring compound in which the carbon atoms are $s{{p}^{3}}$ hybridized state and all the bond angles are equal to the normal tetrahedral angle.
Now considering the statement as;-
Cyclohexane has two conformations i.e. the chair conformation and the boat conformation. In the boat conformation of cyclohexane, all the C-H bonds on the adjacent carbon atoms are in staggered position and there is no steric hindrance or dipole-dipole interactions between the bonded atoms. And it is the most stable conformation of cyclohexane.
But in boat conformation, there is no angle strain as all the bond angles In it are tetrahedral but there is considerable torsional strain and Van Der Waals strain in it and is hence, less stable.
When cyclohexane is dipped in water, it floats on the surface of the water. It is so because the cyclohexane has less density than water and the one which has lesser density will be lighter and thus, floats on the surface of others. Cyclohexane density is 0.77 g/ml and that of water is 1g/ml.
Thus, When cyclohexane is poured in water, it floats because cyclohexane is less dense than water

So, option (b) is correct.

Note:
Conformations are the three-dimensional arrangements in space of the atoms in a molecule which are interconvertible by rotation around a single bond and they cannot be isolated from each other.