Some Basic Concepts Of Chemistry

According to law of multiple proportions when two elements combine to form more than one compound, the fixed amount of one element combining with other element have simple whole number ratio.
[a] and are not example of law of multiple proportion because elements are different.
[b] and are not examples of law of multiple proportion because elements are different.
[c] and
are not example of law of multiple proportion because elements are different.
[d] and NO here 16 parts of oxygen react with 14 and 28 parts of nitrogen. 14:28 is 1:2 which is simple whole number ratio.
It follows law of multiple proportion.

or E = 9