<span>Sodium (Na) is very reactive because it does not have a full valence shell.
For any element, the reactivity is related to how full the valance shell is. If it's not full, but is easily made full, it's very reactive. If it's full, it's non reactive. The valance shell can be filled by either removing the electrons from it, or by adding electrons to it, which ever is the lower number of electrons. So with that in mind, let's look at the available choices and see what makes or doesn't make sense.
Sodium (Na) is very reactive because it does not have a full valence shell.
* This is correct. And because sodium only has 1 electron in its outer shell, it's very reactive since it can lose that electron very easily. This is the correct answer.
Sodium (Na) is very reactive because it does not have enough protons in the nucleus.
* The number of protons simply tells you what element it is, it doesn't have any effect on its reactivity except indirectly by determining how many electrons the atom has in its neutral state. So this is an incorrect answer.
Sodium (Na) is not very reactive because it does not have a full valence shell.
* Sodium is most definitely very reactive. If you don't believe that, just toss a chunk of it into the nearest body of water and see what happens. And since this option is claiming that sodium isn't very reactive, it's obviously wrong.
Sodium (Na) is not very reactive because it can only bond with Chlorine (Cl) to become salt.
* For the same reason that the previous choice was wrong, so is this one wrong.</span>
The correct option is this: SODIUM IS VERY REACTIVE BECAUSE IT DOES NOT HAVE A FULL VALENCE SHELL. For an atom to attain an octet form, it must have eight electrons in its outermost shell. Elements with eight electrons in their outermost shells are un-reactive. Sodium has only one electron in its outermost shell, this makes it to be very reactive because it is very willing to react with suitable elements in order to become stable.
The starch requires a temperature higher than the room temperature (arround 60 °C) to decompose to form simple sugars. This is because the energy required to break the chemical bonds. Also, it may need the action of some specific enzymes (alpha and beta amilase) to break those bonds.
