18) E

Set up algebraic equations for any of the elements present.

e.g. Cu on the left side appears ‘a’ times. Cu appears ‘x’ number of times on the right side.

a = x

However, all of the options has a = x. (Option A has a = 2, x = 2)

Let us try N

b = 2x + 2

Try substituting the values of ‘b’ and ‘x’ from the options given.

Option A cannot be correct.

Option B cannot be correct.

Option C can be correct.

Option D can be correct.

Option E can be correct

Let us make an equation for O

3b = 6x + y + 2

Try substituting the values of b, x and y from the options given.

Option A cannot be correct.

Option B cannot be correct.

Option C cannot be correct.

Option D cannot be correct.

Option E can be correct

So E is the correct answer.