The volume of a sample of gas (2.49 g was 752 ml at 1.98 atm and 62 °c. the gas is

Strategy: with the volume, pressure and temperature you can find the number of moles.

With the number of moles and the mass in grams you can find the molar mass of the gas, and with the molar mass you can figure out the gas.

1) pV = nRT => n = pV / RT

R = 0.082 atm*liter / mol*K
T = 62 + 273.15 = 335.15 K
p = 1.98 atm
V = 0.752 liter

n = (1.98 atm * 0.752 liter) / [0.082 atm* liter / (mol * K) * 335.15K] = 0.05418 mol

2) molar mass = mass / n = 2.49 g / 0.05418 mol = 45.96 g/mol ≈ 46.0 g/mol

So, now you must compare this molar mass with the molar masses of the list of choices.

For example, for NO2 the molar mass is 14 g/mol + 2 * 16 g/mol = 14 g/mol + 32 g/mol = 46 g / mol.

Given that NO2 is in the list of choices, you can conclude that the gas is NO2.

They are like other investigations? say there was a murder u have to do blood test and finger prints which run through a lab.