Answer:
a).
S.I units of length is meters. So we've to change cm → m

b).
km → m

The correct option is D.
Resonance is a phenomenon in which a vibrating system or an external force induces another system to vibrate at greater amplitude at particular frequencies.
When a tuning fork is struck with another object, the tuning fork will start to vibrate as a result of the force that is exerted by the object used to struck it. This type of vibration, without direct excitation by a man is an example of resonance.
Answer:
the mass of the body is 0.02 kg.
Explanation:
Given;
relative density of the oil,
= 0.875
mass of the object in oil,
= 0.013 kg
mass of the object in water,
= 0.012 kg
let the mass of the object in air = 
weight of the oil, 
weight of the water, 
The relative density of the oil is given as;

Therefore, the mass of the body is 0.02 kg.