An ideal gas has volume 
and pressure 
. For this gas, the product 
is given by the expression
where 
is the mass of a molecule of the gas.
State the meaning of the symbol
,
.
A gas cylinder of volume 
contains helium-4 gas at pressure 
and temperature 
. Helium-4 may be assumed to be an ideal gas.
Determine, for the helium gas,
the amount, in mol,
the number of atoms.
Calculate the root-mean-square (r.m.s.) speed of the helium atoms.
