Which two elements have the same number of valence electrons?

Na and Sr
Zr and H
O and S
Mg and P

Which of the following is always a reactant in a combustion reaction? oxygen nitrogen hydrogen carbon

When you mate two plants together the terms is called? answer it fast as possible plz! i have a test tomorrow!

Consider the reaction: n2(g) + o2(g) ⇄ 2no(g) kc = 0.10 at 2000oc starting with initial concentrations of 0.040 mol/l of n2 and 0.040 mol/l of o2, calculate the equilibrium concentration of no in mol/l how would this be done?