`0^o` C and 1 atm refers to standard temperature and pressure, STP.
At STP, 22.4 L contains 1 mole of any ideal gas.
Hence, `560` `cm^3` =` 0.56 L` contains `0.56/22.4` moles = `0.025` moles.
Mass of the sample is 1.60 g.
No. of moles of the sample=0.025
Thus, molar mass of the given sample=`1.60/0.025` = `64` g/mol.
This molar mass matches with the molar mass of `SO_2` i.e
`32 + 2*16` = `64` g/mol.
Therefore, the correct answer is option c).