For 17 the answer is d
for 18 the answer is b
Ionic bond is a compound made up of a meta and a non-metal eg NaCl (sodium chloride)
covalent bond is made up of two non-metals eg H2O (water)
The heat inside the Tupperware causes an increase in pressure and when enough pressure builds, the atoms need somewhere to go and the seal at the top is easiest to break, so the top blows off.<span />
