Which of the following elements contains 7 valence electrons?

Elements: F, Cl, Br, I, At

Explanation:

Hi there,

When you are trying to find the valence electrons for an element, look at the last number of the electron configuration.

For example, if you want to find the number of valence electrons of Carbon (C), you notice that the electron configuration is 2 - 4.

We know that this element has four valence electrons because the last number in its electron configuration is 4.

For your question, simply find all of the elements that have the number 7 as the last number on its electron configuration on the periodic table.

Hope this answer was helpful. Cheers.

Halogens

Explanation:

Because elements can have 8 valence elctrons so noble gas group 18 has 8 valence electrons and previous group before group 18 or noble gas is called Halogens or group 17 whatever you want to prefer periodic table has all of informations

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

2b2t

explanation:

2b2t