1. what do the elements in each group have in common 2. what do the elememts in each period (row) have in common?

I'll assume you are referring to the periodic table

1. The elements in each group have the same number of electrons in the outer orbital.

2. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor.

a boiling water reactor does not boil the water. a pressurized water reactor boils the water faster. a pressurized water reactor is heated directly by the core. a pressurized water reactor does not use fission.