Answer:
none of these are technically correct, but C. is closest? the energy from the sun is radiation, which does not need molecules to travel so its actually B. and C. together? poorly worded
<span>Forward & falling. Hope this helps!</span>
Given :
Initial mass , a = 150 gm .
Half time ,
.
Final mass , x = 18.75 gm .
To Find :
The time taken to decay 18.75 gm .
Solution :
We know , time taken is given by :

Here , k is a constant given by :

Putting all given value in above equation :
We get :

Therefore , time taken is 6.94 hours .
Hence , this is the required solution .