It would be oraganic matter I think.
C) Total Energy = Potential Energy + Kinetic Energy
Explanation:
The total energy of a system (also called mechanical energy) is given by:

where
PE is the potential energy
KE is the kinetic energy
The two types of energy have a different origin:
- Potential energy (PE) is the energy possessed by an object due to its position. It is commonly in the form of gravitational potential energy, which is the energy due to the position of the object in the gravitational field, defined as:

where m is the mass of the system, g the acceleration of gravity, h the heigth of the object relative to the ground
- Kinetic energy (KE), which is the energy possessed by an object due to its motion. It is calculated as

where m is the mass of the system and v is its speed.
Learn more about kinetic and potential energy:
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Answer:
The electric force between them if the pieces of grain are 2 cm apart is
.
Explanation:
Given:
Charge on one grain, 
Charge on another grain, 
Separation between them, 
Electric force acting between two charges
separated by a distance
is given as:

Where,
is Coulomb's constant equal to
.
Now, plug in all the values and solve for
.

Therefore, the electric force between them if the pieces of grain are 2 cm apart is
.
Take a lamina with three holes near the periphery of the lamina, now suspend the lamina through them, one by one. Draw a line of equilibrium for each suspension point. The point of intersection of these three lines would be the centre of gravity.