Subscripts/Ionic compounds?

Question

What subscripts would most likely be used if the following substances formed an ionic compound?

1. An alkali metal and a halogen
2. An alkali metal and a nonmetal from group 6a
3. An alkaline earthmetal and a halogen
4. An alkaline earthmetal and a nonmetal from group 6a
5. a metal from group 3a and a halogen

Answer 1

1. M1X1 (no subscripts), because alkali metals are +1 and halogens -1.
2. M2X1 (subscript 2 for the metal), because group 6a elements are -2 in binary compounds
3. MX2, because alkaline earths are +2.
4. MX (subscripts each 1) because alkaline earths are +2 and group 6a elements -2.
5. MX3, because group 3a metals are mostly +3. An important exception is thallium, which is either +3 or +1. So thallium chloride could be TlCl or TlCl3.