I do not see any possible answers that you have posted. But a good idea would be that it might have fossils, water currents, mud cracks, usually form in shallow seas. Hope this helps!
Answer : The time required for decay is, 84 days.
Explanation :
Half-life of chromium-51 = 28 days
First we have to calculate the rate constant, we use the formula :



Now we have to calculate the time required for decay.
Expression for rate law for first order kinetics is given by:

where,
k = rate constant
t = time taken by sample = ?
a = let initial activity of the sample = 100
a - x = amount left after decay process = 12.5
Now put all the given values in above equation, we get


Therefore, the time required for decay is, 84 days.
Answer:
The technique is called weighing by difference
Answer:
Because a molecule, by definition, has a valence of zero
(neutral charge, stable). Also by definition, an ion has a positive
or negative charge or valence and is not stable.
Explanation:
Some chemical heat highly temperature it was produce poison gas