Expansion joints in masonry walls are provided if length exceeds A. 10 m B. 20 m C. 30 m D. 40 m

The correct answer is: B. 20 m.

Expansion joints are provided in masonry walls to allow for movement due to changes in temperature, moisture, and settlement. The length of a masonry wall that requires an expansion joint depends on a number of factors, including the type of masonry, the climate, and the design of the wall. However, as a general rule, expansion joints are typically provided every 20 m.

Option A is incorrect because expansion joints are typically provided every 20 m, not 10 m.

Option C is incorrect because

Option D is incorrect because expansion joints are typically provided every 20 m, not 40 m.