Which symbol represents a type of electromagnetic radiation released during radioactive decay?
a. 
c.
d.

The correct option is (D) Gamma (  )

Explanation:
Now this question is a tricky one because all of these options are somehow involved in radioactive decay; however, in this case the SYMBOL is required NOT the elements. There are three symbols involved in radioactive decay, which are:
1. α for alpha decay
2. β for beta decay
3. γ for gamma decay 

In the options only one symbol is present which is gamma. Hence option (D) Gamma (  ) is the correct answer.

-i