A researcher studying organic compounds has found that five different molecules - T, W, X, Y and Z-form chains According to the following rules :
i) A chain consists of three or more molecules, though the molecules in the chain are not necessarily different.
ii) T is never found on either end of a chain.
iii) If W appears in a chain, it appears more than once.
iv) X is never found next to Y in a chain.
v) W is never found on the end of a chain unless Z is found somewhere in the chain.
vi) If Y appears in a chain, Z appears also.
Which of the following is a possible chain of molecules?

Options

A. T X Y Z
B. Y T X X
C. W Z T Y
D. W W X Z

Answer

D

Explanation

Screen each choice using the initial conditions. First, all of the sequences meet the minimum-length requirement. Next, we eliminate (1) because I cannot be on the end. Then we eliminate (3) and (5) because if W appears in a chain it must appear more than once. After this we look at (2) and (4) to determine whether or not X is next to Y, and we learn that (2) and (4) both pass this test. Now, we see whether W is on the end of a sequence and, if so, whether Z also appears in the chain. W does not appear in (2) so (2) passes this test. Although W is on the end of the chain in (4), Z also appears, so (4) passes this test. Finally, however, we eliminate (2) because Y appears in (2) without Z and (4) passes this test because no Y appears in (4) at all.