An R.C.C. column is treated as long if its slenderness ratio is greater than A. 30 B. 35 C. 40 D. 50

The correct answer is: A. 30.

A long column is a column that is more slender than a short column. A slender column is a column that is more likely to buckle than a short column. The slenderness ratio is a measure of how slender a column is. It is calculated by dividing the length of the column by the least radius of gyration of the column.

A column is considered to be long if its slenderness ratio is greater than 30. This is because a column with a slenderness ratio greater than 30 is more likely to buckle than a column with a slenderness ratio less than 30.

The other options are incorrect because they are not the correct value for the slenderness ratio of a long column.