It states the fact, which we now know, that electrons are responsible for the chemical bonding. According to this theory, valency is the number of electrons present in the outermost energy shell of the atom. This energy shell is called valency shell.
B. The surface of a silver cup turns black when it is exposed to air.
Half-life is defined as the quantity to reduce to half of its initial value.
Explanation:
The term half-life is generally used in nuclear physics which describes how long a stable atom can survive a radioactive decay or how quickly an unstable stable atom can undergo radioactive decay. Half-life is a constant and does not have any units.
<u>The formula to calculate half-life:
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N(t) = 
Here N(t) is the quantity which is “not decayed”.
is the “initial quantity” of the substance.
λ is the “decay constant”
I believe it is a crystal, read it in a chemistry book over last summer so might be off