what is the effective nuclear chare on electron present in 2 p orbital of nitrogen ?also explain how to calculate it ...

The rule to calculate effective nuclear charge is as follows:
Z_eff = Z- 
Z = atomic number of the given element
 = screening constant.
Screening constant can be found by Slater’s rules which are as follows:

1.The electronic configuration of the given element is written as follows :

(1s) (2s, 2p) (3s, 3p) (3d) (4s, 4p) (4d) (4f) (5s, 5p) (5d)…

2. Electrons to the right of the electron of interest (ns and np group) do not contribute to shielding constant

3. All other electrons in the ns and np group contribute to an extent of 0.35 each to the screening constant except 1s group which contributes to an extent of 0.30.

4. All the electrons in (n-1) th shell contribute 0.85 each to the screening constant

5. All the electrons in (n-2) th or lower shell contribute 1.00 each to the screening constant

For d and f electrons rule 1 to 3 are same.In place of 4 and 5 rule 6 is applicable

6. All the electrons in the groups lying left to the nd and nf group contribute 1.0 each to the screening constant

Following the above rule  can be clculated as follows:
Electronic configuration- (1s²) (2s², 2p³).
Screening constant by ns and np electrons, σ = (0.35 × 4) = 1.4
Screening constant by n-1 electrons = (0.85 × 2) = 1.7
Total value of screening constant = 1.7 + 1.4 = 3.1
Effective nuclear charge, Z* = Z – σ = 7 – 3.10 = 3.90