Arrange the elements in decreasing order of the number of valence electrons

Br,S,Sb,Sr,F,Mg,I,Ca,Na,Kr,Xe,Bi,Ge,Ga,K

A valence electron is an electron in the outside shell. Br has 7, S has 6, Na has 1. Look at the group of the periodic table in which the electron is found. That often tells you the number of valence electrons. I don't know how your are supposed to handle a "decreasing order" when you run into Br with 7 and F with 7 since both are the same.

Here is a good site for you.
http://www.wikihow.com/Find-Valence-Electrons

rye

To arrange the elements in decreasing order of the number of valence electrons, we will need to determine the group number for each element.

The group number of an element indicates the number of valence electrons it has.

Here is the list of elements you provided along with their respective group numbers:

Br (Bromine) - Group 17
S (Sulfur) - Group 16
Sb (Antimony) - Group 15
Sr (Strontium) - Group 2
F (Fluorine) - Group 17
Mg (Magnesium) - Group 2
I (Iodine) - Group 17
Ca (Calcium) - Group 2
Na (Sodium) - Group 1
Kr (Krypton) - Group 18
Xe (Xenon) - Group 18
Bi (Bismuth) - Group 15
Ge (Germanium) - Group 14
Ga (Gallium) - Group 13
K (Potassium) - Group 1

Now, let's arrange them in decreasing order of the number of valence electrons:

1. Kr (Krypton) - Group 18 - 8 valence electrons
2. Xe (Xenon) - Group 18 - 8 valence electrons
3. Br (Bromine) - Group 17 - 7 valence electrons
4. F (Fluorine) - Group 17 - 7 valence electrons
5. I (Iodine) - Group 17 - 7 valence electrons
6. S (Sulfur) - Group 16 - 6 valence electrons
7. Bi (Bismuth) - Group 15 - 5 valence electrons
8. Sb (Antimony) - Group 15 - 5 valence electrons
9. Ge (Germanium) - Group 14 - 4 valence electrons
10. Ga (Gallium) - Group 13 - 3 valence electrons
11. Sr (Strontium) - Group 2 - 2 valence electrons
12. Mg (Magnesium) - Group 2 - 2 valence electrons
13. Ca (Calcium) - Group 2 - 2 valence electrons
14. Na (Sodium) - Group 1 - 1 valence electron
15. K (Potassium) - Group 1 - 1 valence electron

So, the elements in decreasing order of the number of valence electrons are:

Kr, Xe, Br, F, I, S, Bi, Sb, Ge, Ga, Sr, Mg, Ca, Na, K

To arrange the elements in decreasing order of the number of valence electrons, we first need to determine the number of valence electrons each element has.

Valence electrons are the electrons in the outermost energy level of an atom. For elements in groups 1 and 2 (IA and IIA) on the periodic table, the number of valence electrons is equal to their group number.

Here are the elements you provided and the number of valence electrons for each:

Br (Bromine) - Group 17, 7 valence electrons
S (Sulfur) - Group 16, 6 valence electrons
Sb (Antimony) - Group 15, 5 valence electrons
Sr (Strontium) - Group 2, 2 valence electrons
F (Fluorine) - Group 17, 7 valence electrons
Mg (Magnesium) - Group 2, 2 valence electrons
I (Iodine) - Group 17, 7 valence electrons
Ca (Calcium) - Group 2, 2 valence electrons
Na (Sodium) - Group 1, 1 valence electron
Kr (Krypton) - Group 18, 8 valence electrons
Xe (Xenon) - Group 18, 8 valence electrons
Bi (Bismuth) - Group 15, 5 valence electrons
Ge (Germanium) - Group 14, 4 valence electrons
Ga (Gallium) - Group 13, 3 valence electrons
K (Potassium) - Group 1, 1 valence electron

Now let's arrange them in decreasing order of valence electrons:

Kr (8 valence electrons)
Xe (8 valence electrons)
Br (7 valence electrons)
F (7 valence electrons)
I (7 valence electrons)
S (6 valence electrons)
Sb (5 valence electrons)
Bi (5 valence electrons)
Ge (4 valence electrons)
Ga (3 valence electrons)
Sr (2 valence electrons)
Mg (2 valence electrons)
Ca (2 valence electrons)
Na (1 valence electron)
K (1 valence electron)

So the elements in decreasing order of valence electrons are:

Kr, Xe, Br, F, I, S, Sb, Bi, Ge, Ga, Sr, Mg, Ca, Na, K