The correct answer is option 'A' (1828).

Explanation:

The question asks about the calendar that was used in the year 1856. To determine the correct answer, we need to consider the history of calendars during that time period.

1. The Gregorian Calendar:
The calendar most commonly used today is the Gregorian calendar, which was introduced by Pope Gregory XIII in 1582. This calendar was a refinement of the Julian calendar, which had been used since 45 BC. The Gregorian calendar accounted for the slight discrepancy between the solar year and the calendar year, which caused the Julian calendar to gradually drift out of sync with the seasons.

2. Transition from Julian to Gregorian:
The transition from the Julian to the Gregorian calendar occurred at different times in different countries. Catholic countries adopted the Gregorian calendar relatively quickly, while Protestant countries were more resistant to the change. The transition involved skipping a number of days to align the calendar with the solar year.

3. Calendar in the year 1856:
By the year 1856, most countries had already transitioned to the Gregorian calendar. However, there were a few exceptions, such as Russia and Greece, which adopted the Gregorian calendar in the early 20th century.

4. Eliminating the options:
Now, let's eliminate the incorrect options:
- Option 'B' (1850): By 1850, most countries had already adopted the Gregorian calendar, so this option is unlikely.
- Option 'C' (1830): Again, by 1830, most countries had already transitioned to the Gregorian calendar, making this option unlikely.
- Option 'D' (1852): Similar to the previous options, by 1852, the majority of countries were already using the Gregorian calendar.

5. The correct answer:
Based on the above information, the most plausible answer is option 'A' (1828). This means that the calendar used in the year 1856 was the Gregorian calendar, which had been in use for nearly 300 years by that time.