i) Chemical $C_2$ but not chemical $C_1$
ii) Chemical $C_1$ or chemical $C_2$

We are given,

$n\left(U\right)=$ No. of total

skin disorder

$=200$

$n\left(C_1\right)=$ skin disorder due to chemical $C_1$

$=120$

$n\left(C_2\right)=$ skin disorder due to chemical $C_2$

$=50$

Now, $n(C_1\cap C_2)=$ skin disorder due to both the chemical $C_2$ & $C_2$

$=30$

(i)

Now, we have to find the Number of individual exposed to chemical $C_2$ but not chemical $C_1$

i.e $n(C_2-C_1)=n\left(C_2\right)-n(C_1\cap C_2)$

$=50-30$

$n(C_2-C_1)=20$

(ii)

Now we have to find the number of individuals exposed to chemical $C_1$ or chemical $C_2$

i.e.,

$n(C_1\cap C_2)=n\left(C_1\right)+n\left(C_2\right)-n(C_1\cap C_2)$

$=120+50-30$

$n(C_1\cup C_2)=140$