Answer to No.2

a) Enhancement mode

A p-channel MOSFET transistor is Normally-OFF (enhancement mode) if its threshold voltage, VTp, is a negative value.  You can verify this by adjusting the VT in the right-hand side of the applet and observing its value in the lower-right box.

• A MOSFET device is normally-OFF if the device is OFF at zero gate-source bias (Vgs = 0).
• A p-channel MOSFET is ON if Vgs is more negative than VTp (i.e., Vgs < VTp ).
• Thus if VTp = -2.5 V (a negative voltage), then the PMOS is OFF at Vgs = 0 V because Vgs > VTn, and thus it is normally-OFF.