Consider the following equilibrium:

2so2(g) + o2(g) 2so3(g)

which of the following is a correct equilibrium expression?

a.
`"k"_("eq") = (["so"_3])/(["so"_2]["o"_2])`

b.
`"k"_("eq") = (["so"_3]^2)/(["so"_2]^2["o"_2])`
c.
`"k"_("eq") =(["so"_2]["o"_2])/(["so"_3])`

d.
`"k"_("eq") =(["so"_2]^2["o"_2])/(["so"_3]^2)`