What will come in the place of question mark (?) in the

Which chemical is used to generate light to weld metals?

Which of the following cannot be cut by a knife?

Diamond is harder than graphite because of which of the following reason?

Sound cannot pass through –

Acid reacts with metal to form salt and liberates _________ gas.

In a compound, the elements are always present in definite proportions by:

Anesthesia which is administered during the surgeries in the hospitals is a mixture of which of the following gases?

100 gram of ice at 0°C is mixed with 100 gram of water at 80°C. What will be the final temperature of the mixture ?

Which of the following is used as a moderator in nuclear reactors? 

Air coolers are more suitable for –