Which gas has approximately the same density as c2h6 at stp no nh3 h20 so2?

1 mole of any gas occupy 22.4 L at STP (standard temperature and pressure, 0°C and 1 atm).

Let given gases be 1 mole. So their volumes will be the same, 22.4 liters.

Density is the ratio of mass to volume.

By formula; density= mass/volume; d=m/V

To find out masses of gases, do the mole calculation.

By formula; mole= mass/molar mass; n= m/M; m= n*M

Molar masses are calculated as
1. C₂H₆ (ethane)                 = 2*12 g/mol + 6*1 g/mol= 30 g/mol
2. NO (nitrogen monoxide) = 1*14 g/mol + 1*16 g/mol= 30 g/mol
3. NH₃ (ammonia)              = 1*14 g/mol + 3*1 g/mol= 17 g/mol
4. H₂O (water)                    = 2*1 g/mol + 1*16 g/mol= 18 g/mol
5. SO₂ (sulfur dioxide)        = 1*32 g/mol + 2*16 g/mol= 64 g/mol
Use Periodic Table to get atomic mass of elements.

Since their volumes are equal, compounds having the same molar mass will have the same density. 
Recall the formula d= m/V.

Ethane and nitrogen monoxide have the same density.

The answer is C₂H₆ and NO.