**Concept:**
- A
**microstate **is a specific way in which we can** arrange the energy of the system**.
- Many microstates are indistinguishable from each other.
- The more indistinguishable microstates, the higher the entropy.
- The formula for calculating the number of microstates is:

\(= {N! \over (n - r)! r!}\), Where **N = Number of electron positions, r = number of electrons.**

**Calculation:**

- As there are
** 5 orbitals in d, the number of orbitals × electrons = electron positions**
- One electron can occupy two spin states, so positions
**'N' = 5 × 2 = 10**
- The number of electrons
** 'r' = 2**

We know that the number of microstates is given by:

\(= {N! \over (n - r)! r!}\)

Substituting the values in the above equation, we get:

Microstates = \(x = {10! \over (10-2)!\times 2!} =45\)

hence, the number of** microstates in d**^{2} is 45.