Which sample contains the largest number of molecules? a. 100 g of co2 b. 100 g of ch4 c. 100 g of cbr4 d. 100 g of chbr3?

The largest number of molecules  is the same as the largest number of moles of this molecules
to calculate the number of moles you have to divide the mass by the molar mass

molar masses:
CO2:  44,01 g/mol
CH4: 16,04 g/mol
CBr4: 331,63 g/mol
CHBr3: 252,73 g/mol

largest nº of mol= 100/(the smallest molar mass possible)
= 100/16,04
=6,23 moles

all other molecules would be smaller than 6,23 moles because the molar mass is so high.

The answer is B : 100 g of ch4