Question

PLZ HELP!!

Which of the following pairs of elements could possibly be found in the same group on the periodic table?
A forms a 2+ ion; B is an alkaline earth metal.
A is a noble gas; B forms a 1- ion.
A has 3 valence electrons; B is a halogen.
A forms a 2- ion; B has the atomic number 12.

Answer 1

A forms a 2+ ion; B is an alkaline earth metal.

Explanation:

If B is an alkaline earth metal, it is in Group 2. Elements in Group 2 have two valence electrons, so they form M²⁺ ions. Thus, A and B are in the same Group.

2. is wrong. If A is a noble gas it will not form an ion.

3. is wrong. If B is a halogen, it has seven valence electrons.

4. is wrong. If B has atomic number 12, it is magnesium. Mg has two valence electrons and forms Mg²⁺ ions.