The percentage of gold in 24-carat gold is:

The "fineness" of a precious metal item is defined as the weight of fine metal contained within as compared to the overall weight, which includes alloying base metals and any impurities. To make pure metals that lack hardness durable for use in coins and jewellery, alloys are added. Additionally, adding alloys changes colours and lowers the price per weight. For instance, to make the precious metal silver a more resilient alloy for use in coins, metalwork, and jewellery. Millesimal fineness is a technique for indicating the purity of platinum, gold, and silver alloys by parts per thousand of pure metal by mass in the alloy. For instance, "750" denotes an alloy with 75% gold content.

The following words are connected to the precious metal gold's millesimal fitness:
I The purest gold ever created is 999.999, sometimes known as "six nines fine."
The present production of 999.99, or "five nines fine," gold, the second purest form of gold, is a rarity.
The most common gold is 999.9, or "four nines fine".
999, commonly referred to as 24 karat gold and standing for "three nines fine."
The minimal amount of gold permitted in good delivery gold bars is 995.

According to Millesimal fineness, the percentage of gold in 24-carat gold is 99.99.

Hence, the correct option is (A).