Answer:
Both i belive Health class
Answer:
When we cook food in the kitchen, that's the region of higher concentration of the smell. By diffusion, the smell spreads to the whole room and thereby whole house, so anyone standing at a distance, can smell it.
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
, 


<span>When water decomposes into oxygen and hydrogen, the mass "Remains Constant" as according to Law of Conservation of mass, mass can neither be created not destroyed,.
In short, Your Answer would be Option A
Hope this helps!</span>