Which one of the following is not a unit o

Young's modulus $\quad Y =\frac{\text { Stress }}{\text { Strain }}$

As we know, strain is a dimensionless quantity whereas stress is defined as force per unit area.

Stress has units as $Nm ^{-2}$ (SI unit), Dyne $cm ^{-2}$ (cgs unit) or Pascal $( P a)$.

As Young's modulus has same unit as that of stress, thus $Nm ^{-1}$ is not a unit of Young's modulus.