Answer: Option B. -> False
:
B
Archimedes' principle states that the buoyant force exerted on a body submerged in a liquid is equal to the weight of the liquid displaced. Also, the force exerted on a body cannot be compared with a volume, as these are two different physical quantities.

Answer: Option D. -> weight decreases
:
D
The value of acceleration due to gravity is maximum at the surface of the earth. It decreases with increase in height from the surface. It also decreases with increase in depth from the surface. Hence, it is lower in the mine.

Since weight is the product of mass and acceleration due to gravity, it also decreases in a mine.

Answer: Option B. -> Moon revolving round the earth
:
B and D
Centripetal force is the force that comes into picture when a body is moving in a circular path. It acts towards the centre of the circular path, thus changing the direction of motion at every instant. 
In case of moon's revolution, the gravitational force of earth on the moon causes the moon to revolve around the earth. In case of earth's revolution, the gravitational force of the sun on the earth causes the earth to revolve around the sun. Hence, the gravitational force acts as the centripetal force in these two cases.

Answer: Option A. -> $49N$
:
A
Given, mass of a body $m=5kg$ and acceleration due to gravity $g=9.8m{s}^{-2}$.
As we know, weight,
$W=m\times g=5\times 9.8=49N$
Therefore,  weight on the surface of the earth would be $49N$.

Answer: Option B. -> An apple falling on moon
:
B and D

A block falling from a cliff is in free fall under the gravitational force of the Earth and an apple falling on the Moon is under free fall due to the gravitational force of the Moon (since air resistance is negligible in both the cases). A parachute experiences drag force (resistance of air) and thus, another force except gravity acts on it and hence is not under free fall.  An upthrust is used in a rocket during its propulsion due to the continuous expulsion of gases which again renders it not being under free fall.

Answer: Option D. -> All bodies in the universe
:
D

According to the law of gravitation, the force of gravitation between two bodies is directly proportional to their masses and is inversely proportional to the square of the distance between them. Newton's law of gravitation is applicable to all the bodies in the universe. It remains valid everywhere in the universe.

Answer: Option A. -> $15kgf$
:
A

Combined weight of astronaut and his space suit on Earth $=60+30=90kgf$
Since, Moon's gravity is one-sixth of that of the Earth, the weight of the object on Moon is one-sixth of that on the Earth.
$\therefore$ the combined weight of the astronaut and his space suit on Moon is $\frac{90}{6}=15kgf$

Answer: Option B. -> False
:
B

Gravitational force is independent of the medium between the two bodies. Hence, the gravitational force between the Earth and its moon would remain the same irrespective of the medium between the two.

Answer: Option A. -> same in all directions
:
A
In a liquid, pressure acts in all directions equally. Due to this, pressure acts on both the horizontal walls of the container and its base.

Answer: Option B. -> $3.335\times {10}^{-9}$ N
:
B

Given, mass of first body, $m_1=50kg$ and mass of second body, $m_2=100kg$
Distance between the two masses is, $r=10m$.
According to Universal law of gravitation, force of attraction between two bodies is
$F=\frac{G{m}_1{m}_2}{r^2}$
where, $G$ is the gravitational constant and $G=6.67\times {10}^{-11}N{m}^{2}k{g}^{-2}$
$\therefore$ $F=\frac{6.67\times {10}^{-11}\times 50\times 100}{{10}^2}$
$\Rightarrow$ $F=33.35\times {10}^{-10}$ N
$\Rightarrow$ $F=3.335\times {10}^{-9}$ N