Q: throw oneself on a grenade とはどういう意味ですか?
A: The literal meaning is to protect others by covering the grenade with your body. The phrase usually means "to take responsibility/punishment for other people." And is seen as a noble act.
It comes from war time where a soldier would throw themselves over a grenade to protect others, sacrificing themselves.
i.e: "Wow, I can't believe John told the manager he caused the accident when it was really us. He really threw himself on the grenade there."
It's not a phrase you really hear often, and is similar to "To fall on one's sword"


Q: grenade と frag out はどう違いますか?
A: Frag meaning fragmentation


Q: grenadeの発音を音声で教えてください。
A: QAの全文をご確認ください
Q: If i had a grenade, I would throw it to him! この表現は自然ですか?
A: It depends what you're trying to express. If you're angry at someone it would be better to say, "if I had a grenade I would throw it at him." Throwing it to him sounds like he is a friend that you're sharing something with.