Drug E works on

Drug C is used on organism Q. So, drug D also must be used on Q (from condition(iii))

Also, drug A is used on organism R. So, drug B must also be used on R (from condition (iii))

So, we can fill the table like,

Now, organism Q has already been treated with 3 drugs. So, it must not be treated with A and E.

(In condition (ii), it is mentioned an organism can be treated with a maximum of three drugs).

Also, drug B is working on 2 organisms Q and R. So, it must not work on P.

(In condition (i), it is mentioned a drug can work on maximum 2 organisms)

Now, drug B is not working on P, so drug A also must not work on P.

(The reason is if drug A works on P, then drug B must also work on P (condition (iii))

So, we can fill the table upto this,

(Symbol X denotes either drug does not work or the organism was not treated with that drug)

Now in organism P, neither A nor B works.

Now out of the remaining three drugs, only one out of D and E will work (condition (iv)). Also, we need minimum 2 drugs to work (condition (ii)). So, drug C has to work on P.

Now, if drug C works on P, then drug D also has to work on P.

So, now the table will be like:

Now, drug C and drug D are working on organisms P and Q. So they won't work on R definitely.

(condition (i) states, a drug can work on a maximum of 2 organisms)

Also, drug E is not working on P and Q. So, it must work on R for sure.

(condition (i) states, a drug has to work on atleast 1 organism)

So, our final table will be like:

So, drug E works on R.