optical isomer of an alkane

it's 4 because propane can be arranged as both normal and iso....about each one there will be 2 isomers...

sorry it is 4

The 4 different groups are -H, -CH₃, -CH₂-CH₃ and -CH₂CH₂CH₃ attached to give a chiral carbon

The 4 different groups are -H, -CH3, -CH2-CH3 and -CH2CH2CH....So we can have two such situations......and answer is four because one optical isomer can rotate the plane polarised light in equal left and right angle(dextro and laeveo)????