The simple trick which one can consider in such problem where it is asked for positron emission is :
<span>When the atomic number goes DOWN by one and mass number remains unchanged, then a positron is emitted.
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<span>a. </span>

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Here the atomic number decreases by one.
Similarly, options b and d are eliminated.
Option c is also not the answer.
For c, Count the atomic number on left side and compare it with right side. You will see it is 9 on left and 8 on right. Atomic no. did go down by 1. But the atomic mass is changed as well.
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The answer is 3.
Explanation:
It’s the last number and it can’t be 9 because then it would be 48.9 and no 3.
The point at which one drop of base turns the acid indicator into a pink color that lasts for thirty seconds in doing titration is called the end point or the equivalence point.
End point or the equivalence point is the one responsible for the pink color that lasts for thirty seconds.
Many atoms if they are radioactive isotopes will loss protons and neutrons as radiation in order to gain and become more stable
hope that helps