1) Answer is: AlCl3, because aluminum loses three electrons and chlorine gains one electron.
Aluminium chloride is a salt with ionic bonds.
Aluminium (metal from group 13) lost three electrons and form cation with postive charge 3+.
Chlorine (nonmetal from group 17) gain one electronand form anion with negatove charge.
Chemical compound has neutral charge (+3 + 3 · (-1) = 0).
2) Answer is: Al2O3.
Substance made from aluminium and oxygen is aluminium oxide (Al₂O₃).
One formula unit of aluminium oxide has two aluminium atoms and three oxygen atoms.
Aluminium has oxidation number +3 and oxygen has oxidation number -2.
Correct formula for calcium oxide is CaO.
Correct formula for magbesium hydroxide is Mg(OH)₂.
Correct formula for sodium chloride is NaCl.
3) Answer is: The Ca atom should transfer only one electron to Cl, and the second electron should be transferred to another Cl atom.
Calcium cation (Ca²⁺) and chlorine anions (Cl⁻) will form ionic compound (salt) calcium chloride (CaCl₂).
Calcium cations and chlorine anions have a crystal structure in this solid inorganic salt. Ions have the ordered arrangement.
Electron configuration of calcium atom: ₂₀Ca 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².
Atomic number of calcium is 20, it means that it has 20 protons and 20 electrons, so atom of calcium is neutral.
When calcium lost two electrons, it will have 20 protons (positive charge) and 18 electrons (negative charge), which means it has two protons more and it has +2 oxidation number.