Only one of the following atomic notations is written correctly, A.56 26Fe
B.15 7n
C.21 44 Sc
D.36 8F

                     Option-A ( ⁵⁶₂₆Fe ) is the correct one.

Explanation:

                    Atomic Notations are the chemical symbols that shows the atomic number (# of protons) and mass number (# of protons + # of neutrons) of an isotope of an element. It is represented as;

Where;

           X  =  Chemical Symbol of Element

            a  =  Mass Number

            n  =  Atomic Number

Now, we will checkout all provided atomic notation and will find which one is correct and which one is not.

A)  ⁵⁶₂₆Fe:

                  The atomic number for Iron is correct because it contains 26 protons. Also, the mass number is also correct because the most stable isotope (91.57 %) of Iron is ⁵⁶Fe. Hence, this atomic notation is correct.

B)  ¹⁵₇n:

                  The atomic number for Nitrogen is correct because it contains 7 protons. Also, the mass number is also correct because nitrogen has isotope of 0.4% abundance with mass number 15. But, the symbol given is incorrect. It should be capitalized. Therefore, the correct atomic notation will be ¹⁵₇N.

C)  ²¹₄₄Sc:

                  Without going in details we can make this incorrect because it has smaller mass number than atomic number (# of protons). While we know that mass # = $ of protons + # of neutrons.

D)  ³⁶₈F:

                  This is also incorrect because it has 8 protons (atomic number) for Fluorine. Remember, that its the number of protons which gives the identity to particular element. So, in this case we can say that this is the atomic notation of Oxygen because only oxygen carry 8 protons.