Study the given statements P and Q, based on the plasticity index of soils and select the most appropriate option with respect to the correctness of the statements.
P. The plasticity index of a soil is measure of the amount of clay in the soil.
Q. When silt is added to clay, the plasticity index of the resulting soil increases.

Correct option is D

Plasticity:
• The range of water content over which soils remains in a plastic state is known as the
"Plasticity" of the soil.
• Clayey soils exhibit this plasticity property due to the presence of clay minerals. Plasticity Index:
• It is a measure of the plasticity of the soil and is calculated as the difference between the liquid limit and the plastic limit.
• Plasticity index order: clay> silt> sand > gravel
• Adding silt to the clay reduces the plasticity or plasticity index of soil because percentage of clay content is decrease.