The correct answer is: D. Length of column divided by least radius of gyration.
The slenderness ratio is a dimensionless quantity that is used to determine the stability of a column. It is defined as the ratio of the length of the column to the least radius of gyration of the cross-section. The least radius of gyration is the radius of the smallest circle that can be inscribed in the cross-section.
A column with a high slenderness ratio is more likely to buckle than a column with a low slenderness ratio. This is because a column with a high slenderness ratio has a smaller moment of inertia, which means that it is more susceptible to bending.
The slenderness ratio is an important factor in the design of columns. The maximum slenderness ratio that can be used for a column is determined by the material of the column, the type of loading, and the desired safety factor.
The other options are incorrect because they do not take into account the least radius of gyration. The area of cross-section and the radius of gyration are important factors in the design of columns, but they are not the only factors. The least radius of gyration is also important because it determines the stability of the column.