How many questions one should attempt in the entrance test to clear the test with good marks?

There is no fixed number as to the number of questions one should attempt. However scoring around 65 to 70% marks in the test should give you a decent rank to qualify for the GD/PI rounds.

75 correct attempts should be sufficient to clear the cut off, going by the previous year cut off. However you should attempt at maximising your score as it carries 75% weight age in your final selection. Negative marking is also to be kept in mind.