D. Air molecules touch the warm ground, heating them up
Answer:
New volume is 25.0 mL
Explanation:
Let's assume the gas sample behaves ideally.
According to combined gas law for an ideal gas-

where,
and
represent initial and final pressure respectively
and
represent initial and final volume respectively
and
represent initial and final temperature (in kelvin) respectively
Here,
,
,
and 
So, 
So, the new volume is 25.0 mL
It's essentially another word for concentration, of the acid. e.g. "the molarity of the acid is 3moldm^-3"