Which of the following is a valid US amateur radio station call sign?

A valid US amateur radio station call sign follows specific formatting rules set by the Federal Communications Commission (FCC). It begins with one or two letters that signify the station's class, followed by a numeral that indicates a geographic region, and ends with a series of letters that can vary in arrangement.

In the case of the answer provided, "W3ABC" adheres to these rules perfectly. It starts with "W," which is a valid prefix for amateur radio stations in the United States, followed by the numeral "3" indicating a specific region, and concludes with the three letters "ABC," which follow the correct format for amateur callsigns.

This structure is important as it assigns uniqueness while also providing information about the station's location and type. The other options do not fit this structure as required for US amateur radio callsigns; for example, a call sign like "KMA3505" does not conform to the standard because it includes numerals in a manner inconsistent with amateur call signs. Similarly, "KDKA" is a commercial broadcast station call sign, and "11Q1176" does not follow the proper amateur radio format. Understanding these rules helps in identifying legitimate amateur radio call signs in the US.