The radius of the cylindrical iron piece \( (r) = \cfrac{8}{2} \) cm \(= 4\) cm and its height \( (h) = 5 \) cm.
∴ The volume of the cylindrical iron piece:
\(= \pi r^2 h\) cubic cm \(= \pi \times (4)^2 \times 5\) cubic cm.
The radius of the gas jar \(= \cfrac{10}{2} = 5\) cm.
Let the water level rise by \( x \) cm in the gas jar.
∴ According to the condition,
\( \pi \times 5^2 x = \pi \times (4)^2 \times 5 \)
Or, \( 25x = 80 \)
Or, \( x = \cfrac{80}{25} \)
Or, \( x = 3.2 \)
∴ The water level in the gas jar will rise by \( 3.2 \) cm.