I believe the answer is:
1.B.large amount becomes very heavy to carry around
This mean that for making a large purchase, the buyers need to provide additional cost for transportation (providing the space needed to carry the metal to the sellers). This make it easier for that money to be stolen/robbed by bandits in the middle of the journey.
2.B no longer used by many countries
Gold standard refers to a monetary system that is based on a fixed quantity of gold. If the amount of gold held by a country is high, the strength of that country's currency would increase over other country's currency. This system is ineffecient since a country's wealth could also be measured by other resources beside gold.
3.D.they are the same weight and same metal
When we use metal as exchange basis, the value of the coin would be determined by the rarity of the metal and quantitative amount of metal. The rarity usually correlated with the type of the metal (such as gold would be more expensive than iron), and the quantitative amount could be more accurately measured through weight.
4. A 2oz
The trading value is determined by many factors in the gold market, and the amount of weight could be obtained by conducting a simple division.
Currently, gold is traded at $ 800 / Oz
If your current coint had the worth/value of $ 1600 ,
Then the weight of your coul would be :
1600 / 800
= 2 Oz
