# If half-­life of a substance is 5 yrs, then the total amount of substance left after 15 years, when initial amount is 64 grams is Option 1) 16 grams Option 2) 2 grams Option 3) 32 grams Option 4) 8 grams

As learnt in concept

First Order Reaction -

The rate of the reaction is proportional to the first power of the concentration of the reaction

- wherein

Formula:

R            P

a                 0

a-x             x

[differentiate rate law]

Unit of

T1/2 = 5 years

X = 8 gm

Option 1)

16 grams

This option is incorrect.

Option 2)

2 grams

This option is incorrect.

Option 3)

32 grams

This option is incorrect.

Option 4)

8 grams

This option is correct.

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