What are the distinguishing features between standard 3G , 4G and Wi-Fi data connections? Standard implying standards or average speed considered in definition of each. Features like transfer rate and others.
The subject is too broad for a short answer. I suggest you read about the three protocols in Wikipedia:
WiFi in particular is not really comparable to 3G & 4G. It is designed for a short range and to be used locally (within the home, office or internet cafe, rather than in the public sphere), has a multitude of protocols of its own with a range of technologies, speeds, security options etc which don't lend themselves to direct comparison with the other protocols, which are primarily intended for mobile phones and similar devices operating over much greater range of distances and with less end-user options.
Having said all that, we could probably say that 3G is a protocol for mobile phones which has download speeds usually in single digit mbit/sec, 4G is much faster (tens of mbit/sec) and WiFi is usually faster yet (at least with recent equipment) but over a much shorter range. WiFi also requires much more electricity and there are no national WiFi networks that allow free roaming (although some cities offer such a service).
Thanks. Your answer is presented in a disciplined and logical format