The science lab is a production room that unlocks at a vault population of 16 dwellers. Dwellers will produce RadAway in them. Science labs also extend the vault's storage capacities for RadAway. The time it takes to produce RadAway depends on the Intelligence skill of the dwellers working in it. RadAway will reduce the amount of radiation in a dweller by a certain amount.
The output of 3 upgraded double rooms is higher than the output of 2 upgraded triple rooms. The storage capacity and the used space in the vault is the same. That means 3 double rooms are more efficient than 2 triple rooms.