Atoms

Step 1: Definition of isobars.
Isobars are atoms that have the same mass number but different atomic numbers. The mass number is the sum of the number of protons and neutrons in the nucleus. Isobars have different chemical properties because they have different atomic numbers (different elements), but the same mass number.

Step 2: Analyze the options.
- (1) and : These are isotopes of hydrogen, not isobars, because they have different numbers of neutrons but the same atomic number. - (2) and : These are also isotopes of hydrogen, not isobars. - (3) and : These are isotopes of carbon, not isobars, because they have the same atomic number but different mass numbers. - (4) and : These are isobars, because they have the same mass number but different atomic numbers (phosphorus and silicon).

Step 3: Conclusion.
The correct answer is (4), and .

Step 1: Understanding the Concept:
In interference, energy is neither created nor destroyed. It is redistributed from minima to maxima.
Step 2: Detailed Explanation:
Total energy in interference pattern equals sum of energies from individual sources. Bright fringes have more than average energy, dark fringes have less, but total remains constant.
Step 3: Final Answer:
Thus, energy is conserved but redistributed.