معادله ها را موازنه نمایید: (a) $Cr(s) + O_{2}(g) \rightarrow Cr_{2}O_{3}(s)$ (b) $Cu_{2}S(s) + O_{2}(g) \rightarrow Cu(s) + SO_{2}(g)$ (c) $C_{6}H_{5}CH_{3}(l) + O_{2}(g) \rightarrow H_{2}O(l) + CO_{2}(g)$ (a) $Cr(s) + Cl_{2}(g) \rightarrow CrCl_{3}(s)$ (b) $SiO_{2}(s) + C(s) \rightarrow Si(s) + CO(g)$ (c) $Fe(s) + H_{2}O(g) \rightarrow Fe_{3}O_{4}(g) + H_{2}(g)$ (a) $Fe_{2}O_{3}(s) + Mg(s) \rightarrow MgO(s) + Fe(s)$ (b) $AlCl_{3}(s) + NaOH(aq) \rightarrow Al(OH)_{3}(s) + NaCl(aq)$ (c) $NaNO_{3}(s) + H_{2}SO_{4}(aq) \rightarrow Na_{2}SO_{4}(aq) + HNO_{3}(aq)$ (d) $NiCO_{3}(s) + HNO_{3}(aq) \rightarrow Ni(NO_{3})_{2}(aq) + CO_{2}(g) + H_{2}O(l)$ (a) $SF_{4}(g) + H_{2}O(l) \rightarrow SO_{2}(g) + HF(l)$ (b) $NH_{3}(aq) + O_{2}(aq) \rightarrow NO(g) + H_{2}O(l)$ (c) $BF_{3}(g) + H_{2}O(l) \rightarrow HF(aq) + H_{3}BO_{3}(aq)$