How much percentage of absorbed water is used in photosynthesis (in $\%$)?

Which of the following equations is more appropriate for photosynthesis?

In photosynthesis,plants

The hydrogen donor in bacterial photosynthesis is usually

Of the incident solar radiation,__$(A)$__ is photosynthetically active radiation $\text{(PAR)}$. The correct option for the above blank '$A$' is:

What is the actual concentration of $CO_2$ in the atmosphere (in $\%$)?