MHTCET 13 Apr 2026 Shift 1 Paper

Concept:Isobars are atoms of different elements having the same mass number but different atomic numbers.Explanation:Check each pair for equal mass number and different atomic number.For option C, potassium ${ }^{40}\mathrm{K}_{19}$ and calcium ${ }^{40}\mathrm{Ca}_{20}$:Mass number of potassium, $A = 40$Mass number of calcium, $A = 40$So, the mass numbers are equal.Atomic number of potassium, $Z = 19$Atomic number of calcium, $Z = 20$So, the atomic numbers are different.Hence, they satisfy the condition for isobars.Answer:Option C: ${ }^{40}\mathrm{K}_{19}$ and ${ }^{40}\mathrm{Ca}_{20}$