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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How to find net force
The net force is the vector sum of all forces act upon an object.
The formula to calculate net force is Fnet = ma
where the net force is equal to the mass of an object (in Kg) multiplied by the acceleration of the object (in meters per second squared)
You may also calculate the net force acting upon an object with Fnet = Fa + Ff
where the net force is equal to the sum of the applied force and the force of friction.
hope that helped
A patient receiving an X-ray in a hospital
Answer:
CO32−
Explanation:
We have to consider the valencies of the polyatomic ions involved. Recall that it is only a polyatomic ion with a valency of -2 that can form a compound which requires two sodium ions.
When we look closely at the options, we will realize that among all the options, only CO32− has a valency of -2, hence it must be the required answer. In order to be double sure, we put down the ionic reaction equation as follows;
2Na^+(aq) + CO3^2-(aq) ---------> Na2CO3(aq)