Which of the following shows 3 + (x + 6y) rewritten using the associative property of addition?

3 + x + 6y
3x + (6 + y)
x + (3 + 6y)
(3 + x) + 6y

In your given expression, you group x and 6y since they are in parentheses, The associative property tells you that you can change the grouping in an addition.
Don't change the order of the things you're adding, but change just the grouping.

Group the 3 and the x together. Use parentheses.

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table