Explanation: The standard channel spacing assigned for amateur radio VHF FM voice operations, particularly in the popular 2-meter band, is 25 kHz. This spacing allows for efficient utilization of the spectrum while providing adequate separation between channels to prevent adjacent channel interference. Amateur radio generally uses narrow-band FM (NBFM) for voice transmissions, which typically occupy a bandwidth of about 15-20 kHz. A 25 kHz channel spacing accommodates this signal bandwidth, plus a small guard band, without wasting excessive spectrum. Options A and B (10 kHz and 15 kHz) would be too narrow, leading to significant interference between channels. Option D (50 kHz) would be unnecessarily wide for NBFM, resulting in inefficient use of the limited amateur radio spectrum. This 25 kHz standard is widely adopted in repeater coordination plans and general operating practices.