Four tests—Physics, Chemistry, Mathematics and Biology are to be conducted on four consecutive days, not necessarily in the same order. The Physics test is to be held before the test which will be conducted after Biology. Chemistry is to be conducted exactly after two tests are held. Which is the last test to be held ?

The correct option is Mathematics.

Let us analyze the given information step-by-step to determine the order of the four tests: Physics, Chemistry, Mathematics, and Biology, conducted on four consecutive days (Day 1, Day 2, Day 3, and Day 4).

Step 1: Determine the position of Chemistry.
We are given that "Chemistry is to be conducted exactly after two tests are held."
This means two tests take place on Day 1 and Day 2, so Chemistry must be held on Day 3.

Step 2: Determine the positions of Biology and Physics.
We are told that "Physics test is to be held before the test which will be conducted after Biology."
This implies that Biology cannot be the last test (Day 4), because there must be a test conducted after Biology. Additionally, Physics must be held before that post-Biology test.
If Biology were held on Day 2, the test after Biology would be Chemistry (Day 3). For Physics to be held before Chemistry, Physics would have to be on Day 1.
If Biology were on Day 1, the test after Biology could be Day 2. Physics would then need to be before Day 2, which leaves no prior day available for Physics.
Therefore, Biology must be conducted on Day 2, and Physics must be conducted on Day 1.

Step 3: Find the remaining test.
Now we have:
Day 1: Physics
Day 2: Biology
Day 3: Chemistry
Day 4: Mathematics

Thus, the last test to be held is Mathematics.