<u>Answer: </u>He sorted on the basis of average atomic weights.
<u>Explanation:</u>
Dmitri Mendeleev in 1863 arranged chemical elements in the groups according to their average atomic weights.
He said that elements which have similar chemical properties either have similar atomic weights or their atomic weights increases regularly.
Hence, he collaborated a great work in sorting the elements according to their average atomic weights.
Molar mass helium gas :
He = 4.0 g/mol
number of moles: 3.75 / 4.0 => 0.9375 moles
1 mole ------ 22.4 ( at STP)
0.9375 ------ ?
volume = 0.9375 x 22.4 / 1
Volume = 21 / 1
Volume = 21 L
hope this helps!
Both mass and weight are measured by using scales.
