calculate the mass of 48 dm cube of nitrogen gas at R.T.P AND the volume occupied by 4 g of carbon dioxide gas at R.T.P?

At RTP 1 mol gas has volume = 24dm³
You have 48dm³ . This is 48/24 = 2.0mol N2 gas
Molar mass N2 = 28g/mol
Mass of 2 mol N2 = 28*2 = 56g
Answer: Mass of N2 = 56g

Molar mass CO2 = 44g/mol
mol CO2 in 4g = 4/44 = 0.091 mol
1 mol CO2 at RTP has volume 24.0dm³
Volume occupied by 0.091 mol = 0.091/24 = 2.2dm³
Answer: Volume of CO2 = 2.2dm³
Correct to 1 significant figure: Volume = 2dm³