Answer
The number density of particles in the solar corona is $1.09\times 10^{15}~particles/m^3$
Work Step by Step
$PV = NkT$
$\frac{N}{V} = \frac{P}{kT}$
$\frac{N}{V} = \frac{0.03~Pa}{(1.38\times 10^{-23}~J/K)(2\times 10^6~K)}$
$\frac{N}{V} = 1.09\times 10^{15}~particles/m^3$
The number density of particles in the solar corona is $1.09\times 10^{15}~particles/m^3$.
