Answer
(c). $\sqrt (21)$
Work Step by Step
We will use given data about triangle ABC and Pythagoras Theorem to solve for 'b'-
We know that -
$c^{2} =a^{2} + b^{2}$ ( Pythagoras Theorem)
Therefore -
$b^{2} =c^{2} - a^{2}$
$b^{2} = (5)^{2} - (2)^{2}$
$b^{2} = 25 - 4$
$b^{2} = 21$
therefore $ b = \sqrt (21)$
Hence option c is correct
