Not a real diamond, no.
Ruby has a hardness of 9 on Mohs scale of hardness . So any gemstone with hardness more than 9 would scratch a ruby and that includes, diamond, synthetic moizzanite and synthetic diamond.
A diamond can scratch a diamond, but one diamond cannot scratch itself.
No. Only a diamond can scratch another diamond.
gympsum can scratch diamond
A diamond will scratch anything and everything, including another diamond.
A real ruby will scratch just about any mineral except diamond. If it scratches quartz and isn't scratched itself in the process, that's a good (but not definitive) sign.
No. Diamond will scratch steel, however,
A ruby is a ruby; a diamond is a diamond. They are different gemstones. Both occur in nature.
Diamond is NOT like a ruby.
Nope! A diamond is the hardest substance on earth so only a diamond can scratch a diamond!
Yes: not a good use for a diamond, but yes, a diamond will scratch a nail.
Yes, in fact, it is the only way to scratch a diamond.