What is the formula for calculating the efficiency of a heat engine?

The correct answer is .

Explanation:

Heat engine: It is a device which converts the heat energy in to the mechanical work. In heat engine, the heat is transferred from high temperature reservoir to the low temperature reservoir.

It is just opposite of the refrigeration.

The expression of the work done is as follows;

Here, is the heat added to the system and is the heat rejected to the cold reservoir.

The formula for calculating the efficiency of a heat engine is as follows;

Here, W is the work done and is the heat added from the reservoir which is at high temperature and is the heat rejected to the reservoir which is at low temperature.

n has four pairs of electrons in the valence shell, electrons repel one another ,n has 7 protons in its nucleus, and since n has 7 protons, it must fill the second shell, giving it 4 pairs of electrons. the electrons form 3 bonds and 1 lone pair of electrons. each pair of electrons repels the other pairs, so they are equally far apart.

so all of the above

the answer is na (sodium)