K>Mg>Si>C>N>He is the decreasing size of the atoms from largest to smallest.
The size of atoms is usually determined by their atomic radii, which is the distance from the nucleus to the outermost shell of electrons. The size of an atom increases as the number of protons and electrons increases.
The decreasing order of size in these elements is He, C, N, O, Mg, Si, and K. Helium is the smallest atom because it only has two protons and two electrons, while potassium is the largest atom because it has 19 protons and 19 electrons.
Carbon, nitrogen, oxygen, magnesium, and silicon all have between six and twelve protons and electrons, so they are of similar size.
To know more about atomic radius, click below:
https://brainly.com/question/15255548
#SPJ4