C6h12o6 o2 -> co2 h2o what is this formula for?

This is the complete combustion of glucose (C6H12O6). When it is burned in exposure to excess air (hence the O2), it yields gaseous carbon dioxide (CO2), and gaseous water (H2O). 

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.

D. h2o + h2o > h3o + oh- confirmed.