At STP,250cm³of gas had a mass of 0.36g.
1. What result does this give for the molar mass of gas

As we know STP means Standard Temperature and Pressure. Where, Pressure is 1 atm and temperature is 273 K and also Ideal gas law ( PV=nRT) or (PV = w/M RT)

Where –

Now, according to the question –

Calculation –

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i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)