Question

1. Why calcium metal after reaction with water starts floating on its surface?

Answer 1

Calcium even when it's density is 1.55g per cubic metre floats on water because when it reacts with water it forms calcium hydroxide and realeases hydrogen gas .Now this hydrogen gas released during the reaction gets attached to the surface of the metal means to the surface of calcium therefore it appears to float on water.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)

Answer 2

$\huge\underline{\tt{\red{‹ Answer ›}}}$

ᴄᴀʟᴄɪᴜᴍ sᴛᴀʀᴛs ғʟᴏᴀᴛɪɴɢ ʙᴇᴄᴀᴜsᴇ ᴛʜᴇ ʙᴜʙʙʟᴇs ᴏғ ʜʏᴅʀᴏɢᴇɴ ɢᴀs ғᴏʀᴍᴇᴅ sᴛɪᴄᴋ ᴛᴏ ᴛʜᴇ sᴜʀғᴀᴄᴇ ᴏғ ᴍᴇᴛᴀʟ.

$\sf\green{Ca(s) + 2H₂O(l) → Ca(OH)₂ + H₂(g)}$

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