Your question makes no sense. Why is what atom less reactive?? If you're asking why some atoms are less reactive than others then the answer is electron structure and numbers.
Some atoms have more protons pulling on their electrons meaning those electrons will be harder to separate from the atom. You can think of this as a "tug-of-war", if we think of the rope as the most loosely bound electron in each atom then both atoms pull on the electrons, but with different strengths. Either the rope stays almost unmoved, suggesting both atoms are pulling with about the same strength (a covalent bond) or one team completely pulls the rope away from the other, suggesting one atom is a lot stronger (an ionic bond). In terms of reactivity things are a lot more spectacular when one atom is far stronger than the other. More reactive atoms either have a very strong or very weak pull on their electrons. In the case of the "tug-of-war" metaphor the most reactive atoms would be bodybuilders and babies, any average team (or average atom) that pulls against a bunch of bodybuilders will definitely lose and if this average team pulls against babies they'll definitely win. If a bunch of bodybuilders had a tug-of-war with a bunch of babies we'd see a very quick match with a lot more injuries (i.e. a more vigorous reaction).
The other main factor is what is known as "screening". This is the effect of the electrons between the most loosely bound electron and the nucleus on the pull the nucleus exerts on that electron. My chemistry teacher always explains it like this: Imagine you are in a classroom full of students (representing electrons) and the teacher (the nucleus) is at his desk, at the front of the class. It is the teachers (nucleus's) job to keep all his students (electrons) in the classroom (the atom). It is obvious, in this case, that the guy in the back of the class will have the easiest time sneaking out of the class because the teacher has so many students between him and the guy at the back of the class he mightn't even notice that the guy has snuck out. It naturally follows that the fewer rows of seats (electron shells) in the room (atom) the harder it will be for the guy (he's the most loosely bound electron, by the way) to escape to somewhere else. So if there are fewer rows of students between the teacher and student the teacher will see any attempt that student makes to escape and stop it. Similarly, in the atom the more electrons and electron shells between the nucleus and the electron the harder it will be for that electron to escape its grasp.
To put this whole thing as simply as possible the more reactive atoms are the ones that will pull the hardest on electrons or pretty much let the other atom have them, putting up no fight. However, as I've explained above the main reasons an atom would pull hard on or relinquish its electrons are a little bit more complicated.
There are many metals that are more reactive than zinc. To find out which these metals are, you can look at a reactivity series. Some examples of metals more reactive than zinc are sodium, potassium, magnesium & aluminium.
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Transition metals tend to be less reactive than alkali metals or alkaline earth metals. They often form colorful compounds, have multiple oxidation states, and can act as catalysts in chemical reactions. However, some transition metals can still react with certain elements or compounds under the right conditions.
Some are but the most reactive are also non-metals.
It depends on the specific metal and the conditions. Some metals, like alkali metals, are highly reactive and will react readily with air or water. Other metals, like gold or platinum, are much less reactive and do not readily react under normal conditions.
Most metals are reactive to some extent, but their reactivity varies. Some metals, such as gold and platinum, are less reactive and do not easily tarnish or corrode. Other metals, like sodium and potassium, are highly reactive and must be stored in oil to prevent them from reacting with moisture in the air.
There are many metals that are more reactive than zinc. To find out which these metals are, you can look at a reactivity series. Some examples of metals more reactive than zinc are sodium, potassium, magnesium & aluminium.
Silicon is considered to be a relatively reactive element. It reacts with oxygen to form silicon dioxide (silica) and can also react with certain metals and nonmetals to form various compounds. However, silicon is more stable and less reactive compared to some other elements like alkali metals or halogens.
Fireworks that contain metals like strontium, barium, copper, and sodium can produce bright colors when burned. Strontium is an example of a metal used in fireworks that is less reactive than some other metals.
Inert gasses are completely non reactive. The next least reactive would be some where in the middle of the periodic table (probably precious metals).
Mg
Some metals, notably potassium and sodium are highy reactive. Others eg bronze are much less so.
Because some metals are reactive and corrode in sea water
There is no "group" of metals that are unreactive. However, metals that are low on the reactivity series are unreactive. Examples: Gold, Silver, Titanium The Noble gasses are a group on the periodic table that are largely unreactive.
Transition metals tend to be less reactive than alkali metals or alkaline earth metals. They often form colorful compounds, have multiple oxidation states, and can act as catalysts in chemical reactions. However, some transition metals can still react with certain elements or compounds under the right conditions.
The highly reactive non-metals are in the halogen group. They just need one more electron to fill the octet. Therefore they are highly reactive. For example fluorine and chlorine. And the highly reactive metals are placed in the first group (alkali metals). For example Sodium and potassium.
Some are but the most reactive are also non-metals.