What does malluable mean

Which of the following pairs of elements belong to the same groupa. h and he b. li and bec. c and pb d. ga and ge

Ineed to find the answer of this question because i dont understand it

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?