An accurate clock shows 9 a.m. Through how many degrees will the hour hand rotate when the clock shows 7 p.m.?

There are 12 divisions in a clock constituting 360 degree angle, which means that the movement by the hand of the clock in going from one division to the next is $$\frac{360^{\circ\ }}{12}=30^{\circ\ }$$

Our clock hand is going from 9 to 7; the hand would travel from 9 to 12, 3 divisions and then from 12 to 7, 7 more divisions; i.e., in total, the then would travel 10 divisions on the clock, which would make the distance travelled in degrees to be $$30^{\circ\ }\times\ 10=300^{\circ\ }$$

Therefore, Option B is the correct answer.