None. Both chlorines and both hydrogens are single-bonded to the central carbon atom; the molecule is comprised of four single bonds and no double bonds.
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I think it’s the cell membrane if you’re talking about animal cells and plant cells.
The mass decay rate is of the form

where
m₀ = 3000 g,the initial mass
k = the decay constant
t = time, years.
Because the half-life is 30 years, therefore

After 60 years, the mass remaining is

Answer: 750 g