Question

Sodium-24 has a half-life of 15 hours.

How many grams of a 900 g sample will remain after 90 hours?

A) 7.03125 g
B) 7.5 g
C) 14.0625 g
D) 28.125 g

Answer 1

Answer: c 14.0625

Explanation:

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Answer 2

The amount left after 90 hours is 14.0625 g

Explanation:

This is the case of an exponential decay of Sodium-24. The function for exponential decay is,

`y(t)=a(1-r)^n`

where,

y(t) = amount left after time t

a = initial amount = 900 g

r = rate of decay = 0.5 (as the sample is getting halved each time)

t = number of periods =
`(90)/(15)=6` (as we have to convert the period in terms of half lives)

Putting the values,

`y(t)=900(1-0.5)^6`

`=900(0.5)^6`

`=14.0625\ g`