A. Flat model, Mercator projection
Hi
Please find attached file with answers.
Hope it help!
Answer: half life
Explanation: Radioactive decay follows first order kinetics and the time required for the decay of a radioactive material is calculated as follows:

t= time required
k= disintegration constant
x= amount of substance left after time t
a= initial amount of substance
when one half of the sample is decayed, one half of the sample remains and t can be represented as 
at
, 


Are electrons located at the outermost shell of an atom
I have done this question before and even though you didn’t provide the options. I think the correct option is elements