Half life is the time taken by a radioactive isotope to decay by half its original mass. In this case, the halflife of the radioactive isotope is 5000 years.
Initially the mass is 100 %; thus the mass that will be left will be given by;
New mass = Original mass × (1/2)^n where n is the number of half lives;
n = 10000/5000 = 2
New mass = 100% ×(1/2)^2
= 100 % × 1/4
= 25%
Therefore; the mass left after 10000 years is 25% or 1/4 of the original mass.
CH4 + 2O2 =======> CO2 + 2H2O
The peripheral nervous system<span>, or </span>PNS<span>, consists of the nerves and ganglia outside of the brain and the spinal cord. The main </span>function of the PNS<span> is to connect the central </span>nervous system<span> (</span>CNS<span>) to the limbs and organs.</span>
You start by diving each quantity given by the atomic wight of each element:
Phosphorus (P) 
Hydrogen (H) 
Then you divide by the lowest number:
for phosphorus
for hydrogen
So the empirical formula will be:
