Ответ:
алюминия а при варении железа
A) Mr( Na2O)= Ar(Na)*2+Ar(O)=46;
b)Mr(BaCl2) =Ar(Ba)+Ar(Cl)*2=208;
в)Mr( NO) =Ar(N)+Ar(O)=40;
г)Mr(CH4)=Ar(C)+Ar(H)*4 =16.
2) a) CaCl2,б)H2O, в)PH3, г) Ag2O.
<span>H2SeO4 → H2(+1)S(+6)O4(-2)</span>
<span><span>H3AsO4 → H3(+1)As(+5)O4(-2)</span></span>
<span><span><span>HClO4 → H(+1)Cl(+7)O4(-2)</span></span></span>
<span><span><span><span>H3PO3 → H3(+1)P(+5)O3(-2)</span></span></span></span>
<span><span><span><span><span>H2Cr2O7 → H2(+1)Cr2(+6)O7(-2)</span></span></span></span></span>
<span><span><span><span><span><span>H2CrO4 → H2(+1)Cr(+6)O4(-2)</span></span></span></span></span></span>