If you roll two die what is the probability that one die will roll a one and the second die will roll a two?

Assuming you are talking about fair, six-sided dice, then the probability of rolling a 1 on the first roll in 1/6, and the probability of rolling a 2 on the second roll is 1/6. Putting these together, the probability of rolling 1 on the first die and 2 on the second die is 1/36. If you do not care about the order, then you could roll 1,2 or 2,1; in this case the probability would be 2/36, or 1/18.