The correct order of density of the following elements is: (Be, Mg, Ca, Sr) A. Be> Mg > Ca> Cr B. Ca> Mg > Be > Sr C. Ca < Mg < Be < Sr D. Mg < Ca < Sr < Be

To determine the correct order of density for the given elements (Be, Mg, Ca, Sr), we need to refer to their atomic properties. Density is defined as mass per unit volume, so elements with higher atomic masses and smaller atomic volumes will have higher densities.

The atomic masses and atomic numbers (which are indicative of atomic volumes) of the elements are as follows:

Be (Beryllium): Atomic number = 4, Atomic mass ≈ 9.01 g/mol
Mg (Magnesium): Atomic number = 12, Atomic mass ≈ 24.31 g/mol
Ca (Calcium): Atomic number = 20, Atomic mass ≈ 40.08 g/mol
Sr (Strontium): Atomic number = 38, Atomic mass ≈ 87.62 g/mol

Now, let's compare the densities:

A. Be > Mg > Ca > Sr: This order is not correct. Beryllium (Be) has the lowest atomic mass among the elements, so it is expected to have the lowest density.

B. Ca > Mg > Be > Sr: This order is also not correct. Calcium (Ca) has a higher atomic mass and volume than Magnesium (Mg), so it is expected to have a higher density.

C. Ca < Mg < Be < Sr: This order is correct. Among the given elements, Calcium (Ca) has the highest density due to its higher atomic mass and smaller atomic volume. Magnesium (Mg) has a lower density than Calcium but higher than Beryllium (Be), and Strontium (Sr) has the lowest density among the given elements.

D. Mg < Ca < Sr < Be: This order is not correct. Strontium (Sr) has a higher atomic mass than Calcium (Ca), so it should have a higher density.

So, the correct order of density for the given elements is:

C. Ca < Mg < Be < Sr