Will make brainliest if answer correctly.

why would you expect strontium to be chemically more similar to calcium?
they are in the same family/group.
they are in the same period.
they have the same atomic number.
they have the same atomic mass.

They are in same group/family.

Explanation:

Alkaline earth metals are present in group 2 of periodic table. There are six elements in second group. Beryllium, magnesium, calcium, strontium, barium and radium.

All have two valance electrons but in different energy levels. Thus they have similar chemical properties.

Electronic configuration of calcium.

Ca = [Ar] 4s²

Electronic configuration of strontium.

Sr = [Kr] 5s²

They are present in group two and have same number of valance electrons (two valance electrons) and show oxidation state +2 by loosing two valance electrons. They also show similar reactivity.

They react with oxygen and form oxide.

2Sr  +   O₂   →    2SrO

2Ca +   O₂   →    2CaO

this oxide form hydroxide when react with water,

SrO  + H₂O   →  Sr(OH)₂

CaO  + H₂O   →  Ca(OH)₂

With sulfur,

Sr + S   →  SrS

Ca + S   →  CaS