How many electrons are in the highest occupied energy level of a group 5A element?

The thing to remember about a main-group element is that the group number tells you the number of valence electrons said element has.

Main-group elements are located in groups #1#,#2# and #13# through #18#. In your case, the group number is given using the old notation that makes use of Roman numerals to distinguish between main groups, #"A"#, and transition elements, #"B"#.

You thus have

• #"Group 1 " -> " Group 1A"#
• #"Group 2 " -> " Group 2A"#
• #"Group 13 " -> " Group 3A"#
• #"Group 14 " -> " Group 4A"#
• #"Group 15 " -> " Group 5A"#
  #vdots#

and so on.

Now, your element is said to be located in group #5"A"#, i.e. group #15#. For this group, the number of valence electrons is listed in the group number

#"Group"color(white)(a)color(red)(5)"A" -> color(red)(5)color(white)(a)"valence electrons"#

#"Group 1"color(red)(5) -> color(red)(5)color(white)(a)"valence electrons"#

As you know, an element's valence electrons are simply the electrons located on the outermost energy level, i.e. on the highest occupied energy level.

Therefore, you can say that an element located in group #5"A"# has #5# electrons on its highest occupied energy level.