The logic here is
3 x 1.5 = 4.5
5 x 1.5 = 7.5
7 x 1.5 = 10.5
9 x 1.5 = 13.5
In all number pairs except 9 - 15.5, second number is the product of first number and 1.5.
$$\therefore\ $$9 - 15.5 is the odd number pair among the given number pairs.
Hence, the correct answer is Option D
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