Consider a bond between boron and oxygen. which atom would you expect to bear the partial negative charge?

Oxygen is more electronegative than boron. It has more tendency to attract a electron pair while boron is electropositive that means it has more tendency to lose an electron so when there will be a bond between boron and oxygen than boron carries the partial positive charge while oxygen carries the partial negative charge.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

the answer is   c.) 1575 j.

explanation: