Răspuns:
Perioada 2,grupa 2 => Be
perioada 3,grupa 2 => Mg
perioada 4,grupa 2 => Ca
MBeO=9+16=25g/mol;
MMgO=24+16=40g/mol;
MCaO=40+16=56g/mol
Be + 1/2 O2 ---> BeO - oxid de beriliu
1/2 * 32 g O2.......25 g BeO........9 g Be
16 g O2..............x g BeO............y g Be
x = 25 g BeO
y = 9 g Be
Mg + 1/2 O2 ---> MgO - oxid de magneziu
1/2 * 32 g O2.........24 g Mg.......40 g MgO
16 g O2...................a g Mg.........b g MgO
a= 24 g Mg
b= 40 g MgO
Ca + 1/2 O2 ---> CaO - oxid de calciu
1/2*32 g O2..........40 g Ca......56 g CaO
16 g O2.................z g Ca........t g CaO
z = 40 g Ca
t = 56 g CaO
