Answer : The final pressure will be, 666.2 mmHg
Explanation :
Boyle's Law : It is defined as the pressure of the gas is inversely proportional to the volume of the gas at constant temperature and number of moles.

or,

where,
= initial pressure = 790 mmHg
= final pressure = ?
= initial volume = 101.2 mL
= final volume = 120 mL
Now put all the given values in the above equation, we get:


Therefore, the final pressure will be, 666.2 mmHg
And a water molecule, this is called a dehydration synthesis. when 2 molecule combine, a water molecule leave.
Wait, do you mind clarifying what you would like answered for the question?
The molar mass<span> is the </span>mass<span> of a chemical element or a chemical compound (g) divided by the amount of substance (mol).
Hope this helps!</span>