26. Which of the following rocks has high intergranular space to contain fluid but this fluid cannot be shifted because of the high grain size/surface tension effect? Clay Sandstone; Granite Schist.

The porosity is defined as the property of the rock that allows the water to store in its pore spaces. In simple words, it is the measure of the pore spaces that are present in the rock. Whereas the permeability is the property that allows the fluid to pass through the cracks of the rocks and mixing up with the groundwater.

So, in the case of clay, the inter-granular spaces (pore spaces) between the rocks help in trapping the water in them, but they do not allow the water to transmit and get mix up with the groundwater. So, they are the best example of porous rocks.

Hence, the correct answer is option (1).