1) C
2) B
3) A/B not sure
4) C I think
D has a total of four significant figures.
Explanation:
Tollens' reagent is prepared by using two-step process : -
Step 1:
Silver oxide is formed by mixing aqueous silver nitrate with base like sodium hydroxide. The reaction is shown below as:

Step 2
Ammonia solution is drop-wise added until all the silver oxide dissolves to form the reagent. The reaction is shown below as:

Elements in the same group have D. Same number of valence electrons.
Answer:
I am sure that the C one is correct