A student attempts to arrange four elements (as shown below) in order from most reactive to least reactive.

Question

19 12 6 2
K Mg C He
39.10 24.31 12.01 4.00
most reactive least reactive

Is the arrangement correct, and why (or why not)?
(1 point)

Yes. An element's reactivity decreases along with its atomic number.
No. An element's reactivity decreases as atomic mass increases.
Yes. An element's reactivity decreases from left to right on the periodic table.
No. An element's reactivity decreases from right to left on the periodic table.

Answer 1

The arrangement is not correct. The correct reasoning is:

Yes. An element's reactivity decreases from left to right on the periodic table.

In general, in the periodic table, reactivity varies among different groups of elements. For metals, which include potassium (K) and magnesium (Mg), reactivity tends to increase as you move down a group and decreases as you move from left to right across a period. In this case, potassium (K) is more reactive than magnesium (Mg), and both are metals, while carbon (C) is a nonmetal and is less reactive than both. Helium (He) is a noble gas and has very low reactivity.

The correct order from most reactive to least reactive should be:

1. K (Potassium)
2. Mg (Magnesium)
3. C (Carbon)
4. He (Helium)

Therefore, the correct answer should acknowledge that reactivity decreases from left to right across the periodic table, but the original arrangement was not considering that properly.