Sample Frequency - Recommended Practical Nyquist, Lower Used by majorities appications Doubt1: What is the Lowest Sampling Frequency used by majorities sound applications. Is there limited frequency sampling lower than 8KHz In C/C++?

Comment In Java I haven't detected any problem, but using VCL program into one wav sound file (with lower Freq to 8K) was not played, producing Error!

Doubt2: Can I to capture sound using arbitrary Frequency Sampling in C/C++? This process/function/method depends on specific Library? Can I to do this using pure C/C++ Code (without specialized Libraries), where?

Maybe this is a foolish question. I have sound with the 100Hz-500Hz Spectrum.

Doubt3: What is the recommended lowest Nyquist Sampling Frequency (I Know that teorical is two), but is there another practical Criterion? Example: Is recommended to use 2.5, 3 or 4.
In my sound the TEORICAL Nyquist sampling Frequency must be 1KHz.

Thank you
44.1 kHz and 48 kHz are sampling frequencies that are almost always supported by software and drivers but if you need to go lower than that then stop at 8 kHz, as it is commonly supported.