Elements in the same column of the periodic table have what in common?

Elements in same column of periodic table have same properties.

Explanation:

The elements in the same group have same number of valance electrons thus have similar properties.

Consider the elements of group two i.e alkaline earth metals. All have two valance electrons and show similar properties.

Magnesium, barium, calcium etc.

All alkaline earth metals form salt with halogens.e.g,

Mg   +   Cl₂    →    MgCl₂

Ba    +   Br₂    →     BaBr₂

Mg   +   Br₂    →     MgBr₂

Ca    +   Br₂    →     CaBr₂

They react with oxygen and form oxides of respective metal.

2Mg   +   O₂   →    2MgO

2Ba   +   O₂   →    2BaO

2Ca   +   O₂   →    2CaO

these oxides form hydroxide when react with water,

MgO  + H₂O   →  Mg(OH)₂

BaO  + H₂O   →  Ba(OH)₂

CaO  + H₂O   →  Ca(OH)₂

With nitrogen it produced nitride,

3Mg + N₂     →  Mg₃N₂

3Ba + N₂     →  Ba₃N₂

3Ca + N₂     →  Ca₃N₂

With acid like HCl,

Mg + 2HCl  →  MgCl₂ + H₂

Ba + 2HCl  →  BaCl₂ + H₂

Ca + 2HCl  →  CaCl₂ + H₂

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of carbon is as shown here in the image.

a:

by the combination of an unlimited number of elements