The age of father 10 years ago was thrice the age of his son. Ten years hence, father's age will be twice that of his son. The ratio of their present ages is:

7:3

The correct answer is Option (2) → 7:3

Let the present age of the father = $\text{F}$ and the present age of the son = $\text{S}$.

From the question:

10 years ago: Father's age was three times the son's age.

$F - 10 = 3(S - 10)$

$F = 3S - 20 \quad \dots (1)$

10 years hence: Father's age will be twice the son's age.

$F + 10 = 2(S + 10)$

$F = 2S + 10 \quad \dots (2)$

Equating (1) and (2):

$3S - 20 = 2S + 10$

$S = 30$

Substitute into (2):

$F = 2(30) + 10 = 70$

Therefore, the present age ratio is:

$F : S = 70 : 30 = 7 : 3$