The correct answer is A. 120 mm.
The maximum pitch of rivets in tension is given by the following formula:
$p = \frac{t}{2} + 3d$
where:
- $p$ is the maximum pitch of rivets in tension,
- $t$ is the thickness of the thinnest outside plate, and
- $d$ is the diameter of the rivet.
In this case, $t = 10$ mm and $d = 10$ mm. Substituting these values into the formula, we get:
$p = \frac{10}{2} + 3 \times 10 = 120$ mm
Therefore, the maximum pitch of rivets in tension is 120 mm.
Option B is incorrect because it is greater than the maximum pitch of rivets in tension. Option C is incorrect because it is less than the minimum pitch of rivets in tension. Option D is incorrect because it is greater than the maximum pitch of rivets in tension.