Two objects are placed at a certain distance from each other in air. If they are placed at the same distance in water,what is the ratio of the gravitational force between them?

Regarding fundamental forces in nature,the correct statement is

Two identical spheres are placed in contact with each other. The force of gravitation between the spheres will be proportional to ($R =$ radius of each sphere).

Three particles each of mass $m_{1}$ are placed at the corners of an equilateral triangle of side $\frac{L}{3}$. $A$ particle of mass $m_{2}$ is placed at the midpoint of any one side of the triangle. Due to the system of particles,the net gravitational force acting on $m_{2}$ is ($G$ = Universal constant of gravitation).

Mass $M$ is divided into two parts $xM$ and $(1-x)M$. For a given separation,the value of $x$ for which the gravitational attraction between the two pieces becomes maximum is

Explain the vector form of Newton's universal law of gravitation.