The capacity of a certain cuboidal tank is 50000 litres of water.

Capacity of the cuboidal tank $=50000 \mathrm{~L}$

$1000 \mathrm{~L}=1 \mathrm{~m}^{3}$

i. e., $50000 \mathrm{~L}=50 \times 1000$ litres $=50 \mathrm{~m}^{3}$

$\therefore$ The volume of the tank is $50 \mathrm{~m}^{3}$.

Also, it is given that the length of the tank is $10 \mathrm{~m}$.

Height $=2.5 \mathrm{~m}$

Suppose that the breadth of the tank is $b \mathrm{~m} .$

Now, volume of the cuboid $=$ length $\times$ breadth $\times$ height

$\Rightarrow 50=10 \times b \times 2.5$

$\Rightarrow 50=25 \times b$

$\Rightarrow b=\frac{50}{25}=2 \mathrm{~m}$

$\therefore$ The breadth of the tank is $2 \mathrm{~m}$.