Mg (magnesium)
Silicon, which is just below carbon, and Germanium are the two elements that are most like carbon.
This element is probable arsenic.
Mg
The two elements that have the most similar chemical properties to arsenic are Phosphorus (P) and Antimony (Sb).
An atom is the smallest piece of an elemental chemical, a molecule is the smallest piece of a compound chemical (composed of several elements). However due to quantum effects, neither an atom nor a molecule has the properties that we associate with that specific chemical. You need a minimum of several hundred or thousand atoms or molecules in most cases for the "bulk" chemical properties to begin to appear.
Potassium
The element with chemical properties most like silicon is germanium. As an example, both are used in semiconductors.
Calcium is most like magnesium in its chemical bonding properties, with beryllium close behind. These are the elements respectively below and above magnesium in column 2 of a wide form periodic table.
Silicon, which is just below carbon, and Germanium are the two elements that are most like carbon.
Potassium. Sodium is in group1 (period2) the next heaviest element is potassium (period 3). Potassium forms salts with the K+ ion.
The most important is the estimation of chemical properties of an element.
Ar
The chemical properties of calcium are most similar to (in between) the chemical properties of magnesium and strontium.
Mg (magnesium)
The most important criteria is the similarities between chemical properties.
the most important properties in an element is state at room tempreture
There is NOT such an element:All elements have an unique, some more, some less different set of chemical properties, though there are some metals resambling each other more than most of the nonmetals, like oxygen, nitrogen, chlorine, ... etc.