Using a 2cm thick piece of cardboard over a radiation source would be most effective for protecting against which type of radiation?

Idont know. if you want an answer you need to give us some context dude.

Ithink ahopefully im correct 

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

Each calcium ion has a charge of +2, which can also be written as ca2+. if those ions move out of the neuron and no other ions are moving, the neuron would lose the positive charge associated with those ions and become more negatively charged.