Given the mass of the substance is 50g and the density of the water is 1 g/cm³. From the following conditions for which the substance will sink?

Given,
Mass, m = 50 g
If the density of a body is higher than the density of water, it sinks into water. 

Similarly, if the density of a body is lower than the density of water, it floats on water.
The density of the substance given is,
${\Rightarrow \mathrm{d}}_{\mathrm{body}}=\frac{\mathrm{m}}{\mathrm{v}}$

Here, If the value of v is greater than the value of  mass, the density will be less than 1 i.e., less than water and the object will float.

If the value of v is equal to the value of mass, the density will be equal to 1 i.e., equal to water and the object will partially float.

But, If the value of v is less than the value of mass, the density will be greater than 1 i.e., greater than water and the object will sink.
Hence, the correct option would be "If the volume of the substance < 50 cm³".