A Unitless physical quantity is
A. Angle
B. Latent heat
C. Specify gravityD. Density

In geometry, an angle is a figure formed by two rays sharing a common endpoint, called the vertex of the angle.
The minimum heat required to convert a solid into a liquid or vapour, or a liquid into a vapour, without change of temperature is called Latent Heat.
Specific gravity is the ratio of the density of a substance to the density of a reference substance. As it is a ratio it doesn't have any units.
Density is the ration between Mass and Volume.