Elements in the same group/family on the periodic table have similar chemical reactivity because
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Elements in the same group/family on the periodic table have similar  chemical reactivity because  the members of each group in the main group elements has the same number of valence electrons, there are similar properties and similar trends in chemical reactions found in the group

Explanation:

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.

it is the most commonly accepted one