The orthographical projection of a traverse leg upon the reference meridian, is known as

ANS:B - latitude to the leg

From the reference, meridian (N-pole) is = departure of the leg.
Upon the reference, the meridian is = latitude to the leg. If there may reference lines (axis) then departure and latitude both are correct.
But here is reference meridian, so latitude in the leg is correct option. Because meridian is always in a N-S direction. If reference meridian in N-S direction then latitude of the leg and is reference meridian in E-W direction then departure of the leg. I think you are right because it is a general term and the correct answer should be coordinate of the leg. The length of the orthographic projection of a line up on the meridian is the latitude of the line. You think meridian should be only in n-s direction. That's why latitude of leg is correct answer.