Question

for an nmos,if gate and source both are at 5 v,will i get 5volt at drain...?

Answer 1

NMOS turns on when
V(gs) >= V(th)
here V(gs)=0 ( gate and source both at 5V)

so NMOS remains in off state.

Now as for the question 2 cases arise.
1 Drain terminal is open.
2 Drain is connected to a load.

Case1.

here you'll get 5 V at your drain terminal as a MOSFET can be modelled as a controlled linear resistor so if you consider your mosfet to be a resistor you'll get

where left side is source and take right to be drain , now since drain is open you'll get Voltage same as that of source at the drain ( remember what happens with open circuits
)

Case2:

in this case you will get VX at drain terminal because NMOS is in off state (Vgs<Vth) so again an open circuit.

Hope it helps, please forgive my drawing :)