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Q.
The frequency order is for $\gamma$ - rays $(b), X$ - rays $(a)$ UV - rays $(c),$ then
Communication Systems
Solution:
$\gamma$ - rays are most penetrative. They are the fallout of nuclear reaction. $X-$ rays are used for $X-$ raying the human body is rest to $\gamma$ in penetrating. $UV$ rays cannot penetrate the human body but are harmful to the skin. Penetrative power $\propto$ frequency
Thus $U_{\text {gamma }} > U_{X \text { -ray }} > U_{U V}$ or $b > a > c$