What is the mass of 2.90 L of O2 gas at STP

4.16 g

Explanation:

Volume,  V = 2.90 L

STP mans standard temperature and pressure

T = 273 K

P = 1 atm

Mass = ?

Using the ideal gas equation;

PV = nRT

where R = General gas constant = 0.082 L atm mol-1 K-1

n = PV / RT

n = 1 * 2.90 /  (0.082 * 273)

n = 2.90 / 22.386

n = 0.130 mol

The relationship between moles and mass;

Mass = number of moles * Molar mass

Mass = 0.130 mol * 32 g/mol

Mass = 4.16 g

4d^55s^1 ( third choice)