Explanation:
Formula to calculate how many particles are left is as follows.
N = 
where, 
= number of initial particles
l = number of half lives
As it is given that number of initial particles is 
and number of half-lives is 3.
Hence, putting the given values into the above equation as follows.
N = 
= 
= 
or, 
Thus, we can conclude that particles of radioactive nuclei remain in the given sample.
In five hours we've gone through 5 half lives so the answer is:
particles
Explanation:
Filter the sand and sea salt from water.
Add water and wait for sea salt to dissolve.
Filter sand from salt water.
Heat and evapourate salt water for salt.
Covalent compounds don’t always have a bond dipole
Four conditions are needed for natural selection to occur: reproduction, heredity, variation in fitness or organisms, variation in individual characters among members of the population. If they are met, natural selection automatically results.
