The units of Planck's constant are

The correct option is Js.

To determine the units of Planck's constant ($h$), we can use Planck's relation, which connects the energy of a photon ($E$) to its frequency ($\nu$):

$E=h\nu$

Here, the SI unit of energy ($E$) is Joule (J), and the SI unit of frequency ($\nu$) is Hertz (Hz), which is equivalent to per second (s^-1).

Rearranging the equation to solve for Planck's constant ($h$):

$h=\frac{E}{\nu }$

Now, substituting the units of energy and frequency into the rearranged equation:

$\text{Unit of}h=\frac{\text{J}}{{\text{s}}^{-1}}=\text{Js}$

Therefore, the SI unit of Planck's constant is Joule-second ($\text{Js}$).