Q1: The zero atmospheric pressure is at

ANS:E - both (c) and (d) of the above.

In question, it means gauge pressure. When gauge pressure is zero it means this surface has a pressure equal to atmospheric pressure.

So, it means at the water table and at the phreatic surface, pressure is atmospheric (i-e gauge pressure is zero). The term 'phreatic surface' indicates the location where the pore water pressure is under atmospheric conditions (i.e. The pressure head is zero). This surface normally coincides with the water table. On Phreatic Line Pressure head is Zero but atmospheric pressure exists.

Atmosphere pressure is zero at absolute vaccum.