Three numbers are the sides of a triangle if the sum of any pair of numbers is greater than the other number left.
1) since 5+3 is not greater than 18, then this are NOT the sides of a triangle
2)6+17=23>22, 6+22>17 and 17+22>6, then this represents the sides of a triangle
3)16+7=23 is not greater than 24, then this are NOT the sides of a triangle
4)15+8=23 is not greater than 26, then this are NOT the sides of a triangle
In conclusion, the answer is 2)