Answer:E
Explanation:
It is given that Energy of gamma ray is E=1.2 Mev
Shielding effect can be measured by measuring the fraction of gamma rays blocked by shield. If certain thickness will able to block half the radiation then to block 75% radiation we need to add same amount of thickness in order to block the remaining radiation.
i.e. 
fraction is blocked by 10 cm thickness
then remaining radiation is
another 10 cm thickness will block the remaining half radiation i.e. 
so total 75 % radiation will be blocked
A covalent bond is considered covalent
D. compost bins because they recycle matter into a new form
Explanation:
- The law of conservation of matter is about the creation and how matter is being transferred. According to the law, the matter cannot be destroyed. The matter should always be transferred from one form to another in the universe. There is never destruction of matter happens. There is also one more point to it, as it cannot be destroyed it also cannot be created.
- Here in the options, option A tells us the creation which is not possible, option B says about the destruction of matter which is not true according to the law, C is about storing the matter which will not happen because its get transferred and D is the correct option because it talks about the recycle/ transfer of matter.
Displacement/Time = 21m / 15s .
That's choice-D .
