The correct answer is: C. 300 kg/cm2
The compressive strength of concrete is the maximum stress that a concrete can withstand before it fails. It is usually measured in kilograms per square centimeter (kg/cm2). The compressive strength of concrete is affected by a number of factors, including the type of cement used, the water-to-cement ratio, the aggregate type and size, the curing method, and the age of the concrete.
In favorable circumstances, a 15 cm concrete cube after 28 days, attains a maximum crushing strength of 300 kg/cm2. This means that a concrete cube with a side length of 15 cm can withstand a compressive load of 300,000 kg before it fails.
Option A is incorrect because the compressive strength of concrete is typically much higher than 100 kg/cm2. Option B is incorrect because the compressive strength of concrete is typically much higher than 200 kg/cm2. Option D is incorrect because the compressive strength of concrete is typically much higher than 400 kg/cm2.