A pair of dice is thrown simultaneously
$\therefore$ No. of total events (n) = 6 × 6 = 36
Which are
(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6)
(2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6)
(3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6)
(4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6)
(5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6)
(6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)
$\therefore$ Event whose sum is a perfect square are (1, 3), (2, 2), (3, 1), (3, 6), (4, 5), (5, 4), (6, 3)
$\therefore$ m = 7
$\therefore\ \text{Probability}=\frac{\text{m}}{\text{n}}=\frac{7}{36}$