The correct order of density is

We need to determine the correct order of density among the alkaline earth metals Be, Mg, Ca, and Sr.

Recall that the densities of alkaline earth metals (Group 2) are:

$$Be = 1.85 \text{ g/cm}^3$$

$$Mg = 1.74 \text{ g/cm}^3$$

$$Ca = 1.55 \text{ g/cm}^3$$

$$Sr = 2.63 \text{ g/cm}^3$$

Arranging these values in decreasing order gives:

$$Sr (2.63) > Be (1.85) > Mg (1.74) > Ca (1.55)$$

Although atomic mass increases down the group from Be to Ca, the atomic radius increases more rapidly, causing the density to decrease. However, Sr has a significantly higher atomic mass while the increase in volume is not as large, so its density is the highest among these four.

Hence, the correct order of density is $$Sr > Be > Mg > Ca$$, which corresponds to Option C.