How can I understand which valence is applicable in a bond of molecule containing changeable valence?

The twister and runaway train are two coasters at the same amusement park. both coasters start at the same height. the coaster for the twister is twice the mass of the coaster for the runaway train. which roller coaster has greater gravitational potential energy at the start of the ride?

How do you convert 4 mmol of bromobenzene to ml?

In one or two grammatically correct sentences, write a definition for the term molecule geometry