**Answer:**

The law of multiple proportions states that when two elements combine to form more than one compound, the ratios of the masses of one element that combine with a fixed mass of the other element can be expressed as a ratio of small whole numbers.

To determine which of the given compounds can NOT demonstrate the law of multiple proportions, we need to analyze the ratios of the elements in each compound.

**A) NO, NO2:**

- For compound NO, the ratio of nitrogen (N) to oxygen (O) is 1:1.
- For compound NO2, the ratio of nitrogen (N) to oxygen (O) is 1:2.

The ratio of the masses of nitrogen that combine with a fixed mass of oxygen in these compounds is a ratio of small whole numbers (1:2). Therefore, compounds A) NO and NO2 can demonstrate the law of multiple proportions.

**B) CO, CO2:**

- For compound CO, the ratio of carbon (C) to oxygen (O) is 1:1.
- For compound CO2, the ratio of carbon (C) to oxygen (O) is 1:2.

The ratio of the masses of carbon that combine with a fixed mass of oxygen in these compounds is a ratio of small whole numbers (1:2). Therefore, compounds B) CO and CO2 can demonstrate the law of multiple proportions.

**C) H2O, H2O2:**

- For compound H2O, the ratio of hydrogen (H) to oxygen (O) is 2:1.
- For compound H2O2, the ratio of hydrogen (H) to oxygen (O) is 2:2, which simplifies to 1:1.

The ratio of the masses of hydrogen that combine with a fixed mass of oxygen in these compounds is not a ratio of small whole numbers. Therefore, compounds C) H2O and H2O2 cannot demonstrate the law of multiple proportions.

**D) Na2S, NaF:**

- For compound Na2S, the ratio of sodium (Na) to sulfur (S) is 2:1.
- For compound NaF, the ratio of sodium (Na) to fluorine (F) is 1:1.

The ratio of the masses of sodium that combine with a fixed mass of sulfur or fluorine in these compounds is a ratio of small whole numbers (2:1 and 1:1, respectively). Therefore, compounds D) Na2S and NaF can demonstrate the law of multiple proportions.

In conclusion, the compound C) H2O, H2O2 cannot demonstrate the law of multiple proportions as the ratio of the masses of hydrogen that combine with a fixed mass of oxygen is not a ratio of small whole numbers.

Option: D
Na2S & NaF