The correct answer is A. 12t.
The outstand of a flange plate is the distance from the centerline of the web to the edge of the flange. The outstand of a compression flange is limited by the need to prevent buckling of the flange. Buckling is a failure mode in which a structural member fails due to lateral deflection under compressive load. The outstand of a flange plate is limited to a value that will ensure that the flange does not buckle.
The limit on the outstand of a compression flange is given in IS : 800, the Indian Standard Code of Practice for Design of Steel Structures. The code states that the outstand of a compression flange should not exceed 12 times the thickness of the thinnest flange plate. This limit is based on the results of experimental tests that have shown that flanges with an outstand greater than 12t are susceptible to buckling.
The other options are incorrect because they do not represent the limit on the outstand of a compression flange as specified in IS : 800.