A rigid container of neglible heat capacity has one mole of ideal gas if 3cal of heat changes the temperature by1C then the gas may be

1.He
2.Ar
3.O2
4.CO2

More than one options are right

Dear Student , 


Specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of a unit mass of substance through 1ºC. 

so option (3) will be correct here 
Regards