The widely used Whyte notation is a classification method for steam locomotives; it was devised by Frederick Methvan Whyte, and came into use in the early twentieth century. It is based on the wheel arrangement of the locomotive as follows:

[# leading wheels] – [# driving wheels] - [# trailing wheels]

Only the big driving wheels are powered; the unpowered leading and trailing wheels help the locomotive negotiate curves and provide support for different parts of the locomotive.

Some of the common types of classification are also known by names such as those in the answer options:

Atlantic: 4-4-2

Hudson: 4-6-4

Prairie: 2-6-2

Pacific: 4-6-2

The Pacific design is famous worldwide: its introduction in 1901 marked a milestone in locomotive progress. There are different opinions concerning the origin of the name “Pacific.” It may have been in recognition of the fact that a New Zealand designer had first proposed it. Usually, however, new wheel arrangements were named for, or named by, the railroad (railway) which first used the type in the United States. In the case of the Pacific, that was the Missouri Pacific Railroad in 1902.

The magnificent Pacific in the picture is a “Deutsche Reichsbahn” Class 01, rebuilt in the early 1960s and showing clearly the 4-6-2 wheel arrangement.

More Info: en.wikipedia.org