The half life of the substance is 8 hours , Option D is the correct answer.
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What is Half Life ?
Half-life is the time required by an unstable element to reduce to half of its initial value.
The term is commonly used in nuclear physics.
The formula is

N(t) = quantity of the substance remaining
N ₀ = initial quantity of the substance
t = time elapsed
= half life of the substance
The data given in the question is N ₀ = 800 moles , N(t)= 100 , t= 24 hours

Substituting values in the equation


Therefore half life of the substance is 8 hours , Option D is the correct answer.
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Answer:
True statements are 2, 4, 5
Explanation:
They can be broken down by chemical means because we need to break chemical bonds between two (or more) atoms.
They are pure substance because one can't separate them by physical means.
When one separate compounds on two (or more) substances, there are two (or more) different species and they all act differently.
chemical potential energy, thermal energy, electrical energy, sound energy
Explanation:
the coal is chemical potential energy because it is just sitting there, the coal fueled power plant is thermal energy because it is using the heat from the coal to work the power plant, that is then turned into electrical energy, which then goes to the radio which displays sound energy
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The electrons that are in the outermost electron shell, also known as the valence shell, have more energy then those in the inner electron shells, I hope this helps<3