The electricity wouldn't bother you, but;
that's a heavy object - if it should hit you,
and the acid in the battery is quite strong - if it splashed on you.
Unless it hit you, nothing.
ANSWER:No. nine volts isn't enough to harm you. The water would disperse most of the little amount of voltage anyways.
NO unless it was used in a salt water pool even then it is unlikely that it would do any harm in most situations.
I've never tried that, but I am pretty sure the battery would no longer work.
no
once
Nothing. you'd get wet, and the battery would get wet, but noting else unless it was plugged in to something, then you may get shocked.
No
No
No
The sound of a stone hitting the water sounds like PLOP. Be sure to check out The Rapping Buddha on YouTube.
If the magnet is thrown into a pool, it would sink to the bottom due to its weight, assuming it is heavy enough. Magnets are not affected by water, so it would remain magnetic underwater and could pick up any small metallic objects in its vicinity.