What do we mean when we say that the sun is in energy balance?

The amount of energy released by fusion in the Sun's core equals the amount of energy radiated from the Sun's surface into space.

Explanation: Energy balance is a used to describe the balance between the amount of energy input and the amount of energy output. When the amount of energy released is Equal to the amount of energy given back to the System we say there is an energy balance.

The Sun is the major source of energy in the Universe, and it produces energy through FUSION OF RADIOACTIVE MATERIALS IN ITS CORE, WHEN THE ENERGY RELEASED BY FUSION THE SUN IS EQUAL TO THE ENERGY RELEASED TO THE OUTER SPACE WE SAY THERE IS ENERGY BALANCE.

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =

it is b. absorbs thermal energy