A period of 10 years is called what?

• A. Century
• B. Decade
• C. Era
• D. Year

Answer: (B)

Time is counted in named spans, and ten years has its own name: a decade. That's why it fits best. A year is just one year, not ten. A century is one hundred years, which is much longer than ten. An era is a broad, often event-based stretch of time without a fixed number of years. So ten years specifically is called a decade.