Dear student,
The single locant isomers are those that have single location on the carbon chain .The locant is actually a representation of Position of functional group or substitutent on the carbon chain
The two isomers of hexane are
CH3-CH2-CH2-CH2-CH(CH3)--C3 (4 methyl pentane -hexane ) equivalent to 2-methyl pentane
CH3-CH(CH3)-CH2-CH2-CH3 (2-methyl pentane)
regards!