Question

which gas is usually liberated when an acid react with a metal illustrate with an example how will you test for the presence of this gas​

Answer 1

Hydrogen gas is liberated when an acid reacts with a metal. You can feel pop sound when acid reacts with metal. se example in your ncert.

Answer 2

ＨＥＹＡ ＭＡＴＥ !

ᴛʜᴇ ɢᴀｓ ᴛʜᴀᴛ ɢᴇɴᴇʀᴀʟʟʏ ᴇᴠᴏʟᴠᴇｓ ᴡʜᴇɴ ᴀᴄɪᴅ ʀᴇᴀᴄᴛｓ ᴡɪᴛʜ ᴍᴇᴛᴀʟｓ ɪｓ ʜʏᴅʀᴏɢᴇɴ

ｅｘａｍｐｌｅ :-

2ＨＣｌ + 2Ｎａ -----> 2ＮａＣｌ + Ｈ2

hope it'll help you ✌️✌️✌️