What is the value of q when the solution contains 2.50×10−3 m mg2+ and 2.00×10−3m co32−? express your answer numerically?

When q is the concentration of the products / the concentration of the reactants

when the balanced equation of the reaction is:

MgCO3(s) → Mg^2+   +  CO3^2-

so, Q = [Mg^2+][CO3^2-]

and we neglect the concentration of MgCO3(s) as it is in the solid phase.

when [Mg^2+] = 2.5 x 10^-3 m

[CO3^2-] = 2 x 10^-3 m

so by substitution:

Q = 2.5 x 10^-3 * 2 x 10^-3

    = 0.000005 M