Here in this example question, it asks which of the following statements are consistent with Dalton's atomic theory as it was originally stated. So here, we're following just Dalton's first five original postulates. We're not considering the modern atomic theory, which chemists today use through the use of further experimentation and instrumentation. So here, for item 1, nitrogen and phosphorus atoms have the same mass. Remember, Dalton wasn't aware of isotopes. He wasn't aware that different elements could have the same mass number and therefore atomic mass, so this would not be consistent with his original postulates.

Next, all lead atoms are identical. This is almost word for word one of his postulates. He stated that identical elements or atoms should possess the same mass, size, and properties. So this would be consistent.

Regarding item 2, Barium and chlorine atoms combine in a 1:2 ratio to form barium chloride. So the chemical formula for barium chloride is BaCl2. There is 1 barium to 2 chlorines. This is consistent with Dalton's original postulate, where atoms combine in simple whole number ratios.

Then finally, uranium atoms undergo alpha decay to become thorium atoms. This is really talking about radioactive processes, which do occur, but again in Dalton's time, he didn't know that this could happen. So this does not go with one of his 5 original postulates.

So, out of the choices, only option 2 could be consistent with Dalton's original atomic theory. Thus, that would give us option 2 as the correct answer.