The Force Between Two Charged Particles Can Be Calculated Using $F = k \frac { q _ { 1 } q _ { 2 } } { r ^ { 2 } }$

The force between two charged particles can be calculated using the following equation: $F = k \frac { q _ { 1 } q _ { 2 } } { r ^ { 2 } }$ where $\begin{array} { l } F = \text { force in Newtons } \\G = \text { electrostatic constant } \\q _ { 1 } = \text { charge of particle } \# 1 \text { in Coulombs } \\q _ { 2 } = \text { charge of particle } \# 2 \text { in Coulombs } \\r = \text { distance between particles in meters }\end{array}$ What is the appropriate unit for k if the preceding equation is to be homogeneous in units? a. $N$

b. $m ^ { 2 }$

c. $N / C$

d. $\frac { N \cdot m ^ { 2 } } { C ^ { 2 } }$