* Understanding Reactivity: Reactivity with water increases as you move down Group 1 (alkali metals) and Group 2 (alkaline earth metals) of the periodic table. This is because the outer electron is easier to lose as you move down, making the atom more likely to react.

* Ordering the Metals:

* Potassium (K) is the most reactive, followed by

* Sodium (Na)

* Calcium (Ca)

* Lithium (Li) (Lithium is an exception, it's actually less reactive than sodium)

* Magnesium (Mg) (Magnesium is less reactive than the alkali metals).

Therefore, the order from most reactive to least reactive is:

1. Potassium

2. Sodium

3. Calcium

4. Lithium

5. Magnesium

Important Note: These metals react vigorously with water, releasing hydrogen gas and generating heat. Some reactions can be explosive, so it's crucial to handle these metals with extreme caution.