Step 1: State the concept.
The transdermal route delivers a drug through the skin straight into the systemic circulation, completely bypassing the gut and the liver before the drug reaches the body.
Step 2: Recall what first pass metabolism means.
Drugs taken orally are absorbed from the gut and carried to the liver, where a large fraction can be broken down before reaching circulation. This is first pass metabolism, and it lowers oral bioavailability.
Step 3: Connect the route to the problem it solves.
Because skin absorption feeds the drug directly into capillaries, the liver is bypassed. So drugs that suffer heavy first pass loss benefit most from the transdermal route.
Step 4: Eliminate the size and cost options.
Option 2 (bigger molecules) is wrong because the skin only allows small molecules through. Option 3 (costly) is an economic point, not a pharmacokinetic reason.
Step 5: Eliminate the hydrophilic option.
Option 4 (hydrophilic) is wrong because the lipid-rich stratum corneum favours lipophilic, not hydrophilic, drugs.
Step 6: Conclude.
The defining benefit is avoiding hepatic breakdown, so transdermal forms suit drugs that undergo first pass metabolism, option 1.
\[ \boxed{\text{Option 1: Undergoes first pass metabolism}} \]