<u>Answer: </u>
A sample initially contained 150 mg of radon-222. After 11.4 days only 18.75mg of the radon-222 in the sample remained where 3 half-lives have passed
<u>Explanation:</u>
Given, the initial value of the sample, 
= 150mg
Final value of the sample or the quantity left, A = 18.75mg
Time = 11.4 days
The amount left after first half life will be ½.
The number of half-life is calculated by the formula
where N is the no. of half life
Substituting the values,
On equating, we get, N = 3
Therefore, 3 half-lives have passed.
Answer: a substance that increases the hydroxide ion concentration of a solution
Explanation: According to Arrhenius concept, an acid is a substance which donates hydronium ions ![[H^+]](https://tex.z-dn.net/?f=%5BH%5E%2B%5D)
ions when dissolved in water and base is a substance which donates hydroxide ions ![[OH^-]](https://tex.z-dn.net/?f=%5BOH%5E-%5D)
ions in water.
According to the Bronsted Lowry conjugate acid-base pair, an acid is a substance that donates protons and a base is a substance that accepts protons.
According to Lewis concept, an acid is the substance which accepts electron pairs and abase is a substance which donates electron pairs.
Thus a substance that increases the hydroxide ion concentration of a solution is an Arrhenius base.
I think the correct answer from the choices listed above is option B. The correct signs for <span>delta H and Delta S for the production of hydrogen gas by electrolysis of water would be that </span><span>delta h <0 and delta S >0. Hope this answers the question.</span>
Answer:
True
Explanation:
In an ionic reaction, the net ionic equation is used to calculate the standard enthalpy of reaction.
Hence the standard enthalpy of any ionic reaction can be obtained by considering its balanced net ionic reaction equation, hence the answer above.
