The reactivity of an atom is determined by the number of valence electrons it has. Valence electrons are the electrons in the outermost shell of an atom, and they are responsible for chemical bonding. The more valence electrons an atom has, the more reactive it is.

Atom with atomic number 5: This is the element boron (B). Boron has 5 electrons, with the electronic configuration 2,3. This means that it has 2 electrons in the first energy level and 3 electrons in the second energy level. The three electrons in the second energy level are valence electrons. Boron is a metalloid, meaning it has properties of both metals and non-metals. It is relatively unreactive compared to most metals, but more reactive than most non-metals.

Atom with atomic number 10: This is the element neon (Ne). Neon has 10 electrons, with the electronic configuration 2,8. This means that it has 2 electrons in the first energy level and 8 electrons in the second energy level. The eight electrons in the second energy level are valence electrons. Neon is a noble gas, meaning it is very unreactive. It is the least reactive of all the elements.

Therefore, the reactivity of atom with atomic number 10 (neon) is much lower compared to atom with atomic number 5 (boron).