"cg" is centigram, which is one-hundredth of a gram.
I will first convert from g to cg (multiply by 100), then from mL to L (multiply by 1000).

There are four type of intermolecular forces: ionic, dipole-dipole, hydrogen bonds and London disperssion forces.
CH4 have no ions, so there are not ionic forces.
CH4 is a symetrical molecule, so there cannot be a net dipole in the molecule, so there is not dipole-dipole interaction.
Hydrogen bonding is only possbile when H is bonded to N, O or F, beacuse they are the atoms that considerable higher electgronegativy than hydrogen.
So, the only intermolecular force present in CH4 molecules is London disperssion forces, which is a force present in any molecule and is the weakiest one. That explains the low melting and boiling points of CH4.
.2135 mol of Ba(OH)2 are needed to neutralize .427 mol of 2HC2H3O2