If the passing of five half-lives leaves 25.0 mg of a strontium-90 sample, how much was present in the beginning

initial amount = 800 mg

Explanation:

Given data:

Amount of strontium-90 after 5 half life = 25 mg

Total amount of sample = ?

Solution:

At 5th half life = 25 mg

At 4th half life = 25× 2= 50 mg

At 3rd half life = 50×2 = 100 mg

At 2nd half life = 100×2 = 200 mg

At 1st half life = 200×2 = 400 mg

when time 0 = 400×2 = 800 mg

Conformation:

initial amount = 800 mg

1st half life = 800/2 = 400 mg

2nd half life = 400/2 = 200 mg

3rd half life = 200/2 = 100 mg

4th half life = 100/2 = 50 mg

5th half life = 50 /2 = 25 mg

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance

if you mean hydrogen and oxygen then water is the product