Here Option 1 can be the answer but in key option 2 is given

Option 2 is correct
Kindly clarify.

Dear student, Phosphorus is a constituent of cell membrane as it is found as phospholipid layer in cell membranes, while it is present in all(not in certain) nucleic acids as a phosphate group and it is not present in all proteins. While all the other three options are correct statements in terms of facts. Since we need to find the incorrect statement so option 2 is correct. Thanks and regards.