Minimum grade of concrete to be used in reinforced concrete as per IS: 456-1978 is

Answer: Option B

As per IS: 456-1978, the minimum grade of concrete required for reinforced concrete (RC) structures is M20.

The M20 grade concrete has a characteristic compressive strength of 20 MPa after 28 days of curing.

Lower grades like M15 and M10 are generally used for plain cement concrete (PCC) and are not suitable for reinforced structures.

Higher grades such as M25 and above are used for structural members requiring higher strength.

Hence, the correct answer is M20 (Option B).