Why is (±) butane-2-ol is optically inactive?

cbse
haloalkanes

#1

(ii) (±) butane-2-ol is optically inactive as it exists in
two enantiomeric forms, i.e. (+) and (-) forms, and these are non-superimposable mirror images of each other. Both of them are present in equal amounts, which cancel the optical rotation of each other as (+) butane-2-ol rotates the plane polarised light towards right and’ (—) butane-2-ol rotates the plane polarised light towards left to the same extent. Therefore, the overall rotation is zero and hence, (±) butane-2-ol is optically inactive.