Answer:
question 1- is B
question 2- is A
*I hope this helps you guys out!
Answer:
11.02 % of an isotope will be left after 45 seconds.
Explanation:

where,
= initial mass of isotope
N = mass of the parent isotope left after the time, (t)
= half life of the isotope
= rate constant
We have :
Mass of Beryllium-11 radioactive isotope= 
Mass of Beryllium-11 radioactive isotope after 45 seconds = 
t = 45 s
= rate constant = 

Now put all the given values in this formula, we get


Percentage of isotope left :

11.02 % of an isotope will be left after 45 seconds.
Answer:
1. KBr
2. 2NH4OH
3. 2NO3
Explanation:
You just need to work backwords and take them step by step.
- Please let me know if these are right, if not I will correct them. Also, if you have any questions pertaining to any of this, let me know, and I will be happy to try and answer them.