Final answer:
The uninhabited islands claimed by Portugal in 1431 and now home to a quarter million people are the Madeira Islands (D). Portuguese explorers expanded their maritime empire by settling in the Madeira Islands, the Azores, and other territories.
Step-by-step explanation:
The correct answer to the question is D) Madeira. These islands were discovered by Portugal in 1418 and claimed soon after. Portuguese sailors were the first to land on the uninhabited Madeira Islands, which now boast a population of around a quarter million people. The Azores, another group of islands claimed by the Portuguese, were discovered in 1431 and were also initially uninhabited. Portuguese explorers not only settled these island groups but extended their influence to areas such as the Cape Verde Islands and the coast of Africa.
Portugal's efforts in establishing colonies in the Atlantic and their exploration down the west coast of Africa highlight their significant role in the era of Atlantic exploration. This expansion was a precursor to their engagements with territories further afield, establishing a pattern of Portuguese maritime empire that would extend across the globe.