This question generates more confident advice than almost any other, most of it based on what worked for the person giving it. The honest answer is that the right order depends on you, and a mock test will tell you in an afternoon what debate will not settle in a month.
The case for Biology first
Ninety questions, largely recall, and the section where a prepared candidate moves fastest. Starting here banks marks early and buys time for Physics. It also starts the paper with success, which matters more than it sounds — the first ten minutes set the tone for the next 190.
The case against Biology first
Fast progress early can produce complacency, and Physics attempted with 50 minutes left and rising panic goes worse than Physics attempted fresh. If your Physics is shaky, doing it while you are calm is worth more than doing it with marks already banked.
The case for hardest-first
You are sharpest at the start. Spending that sharpness on the section that needs it, and leaving recall for when you are tired, has a real logic — retrieving a memorised fact degrades less under fatigue than a three-step derivation does.
How to actually decide
Take three full-length mocks in different orders. Same conditions, same time of day, different sequence. Then compare not just the total but:
- Marks per section in each order.
- Where time ran out.
- How many careless errors appeared in the final 40 minutes.
The last one is the most revealing and the least examined. An order that produces a marginally lower score but three fewer late-paper errors is usually the better order, because the errors are what scale badly on a hard paper.
Then stop changing it
Once you have an order, keep it for every remaining mock. The benefit comes from the sequence being automatic — one fewer decision to make in a room where your judgement is already under load.
Changing your approach on exam day, having practised another, is how a well-prepared candidate produces a surprisingly bad paper.