which type of seeds float on the surface of water when put in water and why ?
for class 8th
short answer question
Answers
Explanation:

For all other seeds in between, the best length of time to leave seeds in water is more an art than a science. You want to soak them long enough so the coats begin to swell, but not so long that they just split or rot.
A safe place to start is a couple of hours; after that, check your seeds every hour until you start to see them plump up.
Anecdotal evidence abounds for people who have soaked seeds for up to 24 hours without issue (such as the case with okra), but this is really a matter of try-and-see.
Why do some seeds float or sink while soaking?
When you start soaking your seeds, you might find a few floaters.
Contrary to popular belief, this does not necessarily mean the floating seeds are “bad.” They’re soaked for such a short period of time that it isn’t possible to tell whether or not they’ll germinate — sometimes they will.

Answer:
Arabidopsis seeds rapidly release hydrophilic polysaccharides from the seed coat on imbibition. These form a heavy mucilage layer around the seed that makes it sink in water.