The density has been given as the mass of the substance per volume of the solution. The mass of citric acid in the bottle has been 1.22 grams.
<h3>What is percent mass?</h3>
Percent mass can be given as the mass of substance in the total mass of the solution.
The volume of the face serum has been 250 mL, and the density is 0.979 g/mL.
The mass of face serum in the bottle has been:

The total mass of face serum has been 244.75 grams.
The percent mass of citric acid in face serum is 0.5%. This states the presence of 0.5-gram citric acids in 100 grams sample.
The mass of citric acid in the face serum sample is given as:

The mass of citric acid present in 250 mL serum sample has been 1.22 grams.
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The element with atomic number 71(lutetium) is paramagnetic
This is because all its electrons is not paired . lutetium has electron configuration of (Xe) 4f^14 5d^1 6S^2
Its 5d sub shell is not paired since the d sub shell can accommodate a total of 10 electrons hence lutetium is paramagnetic