When the switch is turned on, a wire connects the anode to the cathode. Do batteries require any energy to start the redox reaction? If not, what causes the electrons to transfer from one species to another?

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.

If your on odysseyware i believe the answer would be c. 

Descriptive investigations are mainly questions to uncover information. it does not have an hypothesis. it's mainly gathering information, it is not repeatable as you are just asking questions.