Why do rivers have deltas?

A delta is formed when the river deposits its material faster than the sea can remove it. ... Cuspate - the land around the mouth of the river juts out arrow-like into the sea. The Ebro Delta. Bird's foot - the river splits on the way to the sea, each part of the river juts out into the sea, rather like a bird's foot.

I hope it's helpful!

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.