The half-life of sodium-25 is 1.0 minute. Starting with 1 kg of this isotope, how
much will remain after half an hour?

Explanation:

k

=

0.693

t

1

2

On putting the value of half-life, we get:

k

=

0.693

1

=

0.693

(

min

)

−

1

First order rate law can be written as:

k

=

1

t

ln

a

0

a

t

Where,

k is rate constant

t is time required for decay

a

0

is the initial amount

a

t

is the amount left at time t.

On putting the values, we get:

0.693

=

1

30

ln

1

a

t

Therefore,

ln

1

a

t

=

0.693

×

30

a

t

=

9.35

×

10

−

10

k

g

9.35

×

10

−

10

k

g

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.