Question

The weight of the body is maximum in
A. Air
B. Hydrogen
C. Water
D. Vacuum

Answer 1

Hint: When a body is placed in a medium, two forces are acting on it namely Gravitational force and Buoyant force, both of these forces act in opposite directions so the net weight of the body is the difference of these forces.

Complete step by step answer:
The buoyant force is the upward force acting on a body by a liquid or gas when the body is immersed in the liquid or gas partly or completely.
Now, according to Archimedes’ principle, when a body is immersed in a liquid or gas partly or completely, there is some loss in the weight of the body and the loss in weight is equal to the weight of liquid or gas displaced by the immersed part of the body.
So when a body is placed in a medium its resultant weight = Gravitational force – Buoyant force.
So for the maximum value of the weight, the buoyant force has to be minimum.
There is no buoyant force in a vacuum so the weight of the body is maximum in the vacuum.

So, the correct answer is “Option D”.

Additional Information:
The buoyant force is also called upthrust. It is equal to the product of the mass of displaced liquid or gas and gravitational acceleration.
Weight is the force exerted on a body by gravity. Weight of a body is expressed as,
$W = mg$ where $W = $ weight of the body, $m = $ mass of the body and $g = $ gravitational acceleration. (Gravitational acceleration is the free-fall acceleration of a body in the vacuum)

Note:
The buoyant force depends on the density of the liquid or gas. As the density of liquid is higher than that of gas, the buoyant force is higher in liquid than air. Now hydrogen has only 7% of the mass of air so it is less dense than air that’s why the buoyant force due to the hydrogen is lower than that due to air.