Answer: a. 0.8 tons p. month.
Explanation:
Given: Total nuclear waste = 60,000 metric tons
Time take = 60 years = 12 x 60 months [ 1 year = 12 months]
= 720 months
Total nuclear power plants = 104
Now , Average waste produced by each plant = 

Hence, 0.8 tons p. month is produced by each plant.
So, option a. is correct.
Each aluminium ion should have a charge of +2, because the sum of oxidation numbers must be zero.
The uncharged aluminium atom must lose two electrons to become an ion with +2 charge.
If you find some mistakes in my answer, please let me know!
Answer: (3)
Medeleev arranged elements in order of increasing atomic weight and similar properties
He noticed that similar elements were grouped together by using this.