You have two solid substances that look the same. what measurements would you take and what tests would you perform to determine whether they actually are the same

The easiest way to go about this would be to check out their physical properties. Physical properties are those attributes of a substance or material that can be observed or measured without altering or changing the composition of that material.

So we can check out the following physical properties:

1. Color. Check if there is any difference in color.

2. Weight. If possible, take similar sized pieces of the two and note any difference in weight .

3. Texture. Are they smooth or rough to the touch?

4. Smell or odor. Check out any unique smell.

5. Solubility. Dissolve a bit of each in water and see how soluble each is.

6. Melting point. Carefully heat a piece of it and see if they will melt, and if so at what temperature.

7. Pliability. Can any of them bend, are they flexible?

8. Magnetism. Can the be attracted by a magnet?

9. Bouyancy . Can they float on water?

10. Electrical conductivity. using a battery and small torch bulb, find out if they can conduct an electric current.

These 10 physical tests can help differentiate between the two materials. There are  still many more that can  be safely carried out.

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.