2. write the formula for the compound formed by each pair of elements.\na. calcium and sulfur \nb. magnesium…

Explanation:

Step1: Determine ion charges

Calcium (Ca) forms a $Ca^{2 + }$ ion and sulfur (S) forms a $S^{2 - }$ ion.

Step2: Write the formula

The charges balance out, so the formula is $CaS$.

Step3: Determine ion charges for magnesium and iodine

Magnesium (Mg) forms a $Mg^{2+}$ ion and iodine (I) forms an $I^{-}$ ion.

Step4: Write the formula

To balance the charges, we need 2 iodine ions for 1 magnesium ion, so the formula is $MgI_{2}$.

Step5: Determine ion charges for aluminum and chlorine

Aluminum (Al) forms an $Al^{3+}$ ion and chlorine (Cl) forms a $Cl^{-}$ ion.

Step6: Write the formula

To balance the charges, we need 3 chlorine ions for 1 aluminum ion, so the formula is $AlCl_{3}$.

Step7: Determine ion charges for barium and oxygen

Barium (Ba) forms a $Ba^{2+}$ ion and oxygen (O) forms an $O^{2 - }$ ion.

Step8: Write the formula

The charges balance out, so the formula is $BaO$.

Answer:

a. $CaS$ b. $MgI_{2}$ c. $AlCl_{3}$ d. $BaO$