Answer
(c) iron and rock and some lighter elements
Work Step by Step
The density $ρ$ can be defined as $\frac{mass}{volume} = \frac{m}{V}$
We know that the volume V of a sphere of radius R is $V = \frac{4}{3}πR^{3}$
Calculating directly . . .
$ρ' = \frac{m}{V} = \frac{m}{\frac{4}{3}πR^{3}} = \frac{7.9m_{earth}}{\frac{4}{3}π(2.3R_{earth})^{3}} = 0.65\frac{m_{earth}}{\frac{4}{3}πR_{earth}^{3}} = 0.65ρ_{earth}$
So the density of the exoplanet is 0.65 times the density of the earth. From the table provided, we see that densities within this range indicate that the planet has a core of iron, rock, and other lighter elements. Therefore, the correct option is (c).
