The different forms of a gene that decides a characteristic are known as Alleles.
A feature that has different forms in a population are Characteristics.
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To find the density, the formula would be d= m/V. Your answer would be 19.9 or if you round, 20.
Dimension of the salt crystal is:
Length = 3.22 x 10^-2 cm
Breadth = 1.5 x 10^-4 cm
Height = 4.30 x 10^-3 cm
So it is cuboidal in shape.
Volume = L × B × H