In this question, we are given two positions of a dice, one when 1 is at the bottom and the other position is not mentioned. We need to determine what number will be on the top when 1 is at the bottom.

To solve this, let`s analyze each option:

Option 1: If 3 is on the top, it means that the opposite side of the dice should show 1. However, this contradicts the given condition that 1 is at the bottom. Therefore, option 1 is incorrect.

Option 2: If 5 is on the top, the opposite side should show 2. Again, this contradicts the given condition that 1 is at the bottom. So, option 2 is incorrect.

Option 3: If 6 is on the top, the opposite side should show 1. This satisfies the given condition that 1 is at the bottom.

Option 4: The option states "Cannot say," indicating that we do not have enough information to determine the number on the top. However, based on our analysis of the previous options, we can conclude that option 4 is incorrect.

Therefore, the correct answer is option 3, where 6 will be on the top when 1 is at