Is it true that Dalton was unable to explain the concept of isobars and isotopes?

 

The given statement is true.

• According to Dalton's Atomic Theory,
  Atoms of same elements are similar in all respects. Atoms of different elements are different in all respects.
• But later it was found that isotopes and iso bars also exist. 
• Isotopes are the atoms of same element having same atomic number but different mass number.
• Isobars are the atoms of different elements which have same mass number but different atomic number.
• Therefore, Dalton was unable to explain the concept of isobars and isotopes because he assumed atom as the smallest indivisible particle. He did not know about electrons, protons, and neutrons.