The emissivity of an ideal reflector has which of the following values?
a. 0
b. 1
c. 100
d. infinity

Emissivityis a measure of how much thermal radiation a body emits to its environment. On the other hand we have that reflectivity is a measure of how much is reflected, and transmissivity  is a measure of how much passes through the object. If a body is required to be ideally reflective to its maximum efficiency, the body should NOT have the property of transmissivity or emissivity. Therefore it should be 0 its emittivity.

Correct answer would be A : ZERO.

d. learned preferences i believe is your answer

fgravity=10x10=100n case 1

fgravity=30x20=600n case 2

6 times more