Final answer:
If a currency becomes less valuable in world markets, its price falls, and this decrease is known as depreciation. Hence, 'less valuable' corresponds to depreciation of the currency.
Step-by-step explanation:
When a currency becomes less valuable in world markets, then its price falls, and this decrease is called depreciation. So, the correct answer to the question is b. less; depreciation. This concept is fundamental to understanding how currencies interact with one another on the international stage.
When the exchange rate for a currency rises, meaning the currency exchanges for more of other currencies, we refer to this as appreciating or "strengthening." Conversely, when the exchange rate for a currency falls, and it trades for less of other currencies, it is referred to as depreciating or "weakening." Understanding these terms is crucial for anyone interested in international business, economics, and finance.