Fill the missing number to make it a magic triangle.

1. 6

The correct option is A 6
Let's add the numbers on each side of the triangle.

1 + 5 + 3 = 9
3 + 4 + 2 = 9
1 + ? + 2 = 9

3 + ? = 9
? = 9 - 3
= 6

So, the missing number on the magic triangle is 6.