GGY has answered all five questions correctly, precisely, and spontaneously! whee!

Answers:

1: 500kg
2: Thermal expansion of water, and to a lesser extent, melting of polar ice caps
3: The oxygen attached to the carbon within the -COOH group, being highly electronegative, draws electrons away from the OH bond, weakening it and allowing the proton to be lost more easily. After the loss, the excess electron is shared by the two highly electronegative oxygen atoms, rendering the ionised state stable, making it less likely for the proton to return to the carboxilate ion.
4. Theory of relativity (GGY gave "Does the Inertia of a Body Depend Upon its Energy Content?". Frankly speaking I had never heard of it before he gave it as the answer. I checked and found that this was the very paper which Einstein published his e=mc² thing. Considered that answer correct.)
5. Cervical Vertibrae

GGY r0XX0rz.

he wud pWnzz j00 in th30ry and pr4kt1c4l.

ph34r t3h GGY.

(but of course amyas pwnz him in theory, just like he pwnz everyone else who is 8/7 times his age)