If m denotes the number of $5$ digit numbers if each successive digits are in their descending order of magnitude and n is the corresponding figure, when the digits are in their ascending order of magnitude then $(m-n)$ has the value?

$\textbf{Step-1: For descending order}$

$\text{In this case, we can choose 5 numbers from 10 numbers.}$

$\text{This can be done in}$ $^{10}C_5$ $\text{ways.}$

$\text{Now, as there is only one way in which five numbers can be arranged,}$ $m=^{10}C_5.$

$\textbf{Step-2: For ascending order}$

$\text{In this case, we have 9 options to choose from, as here, 0 will be in front and the }$

$\text{number will be 4-digit.}$

$\text{Hence,}$ $n=^{9}C_4$

$\textbf{Step-3: Finding}$ $\mathbf{m-n}$

$m-n=^{ 10}C_5-^9C_4$

$=^9C_5$

$\textbf{Hence, the correct option is (B).}$