The isotope U-235 is important because under certain conditions it can readily be split, yielding a lot of energy. It is therefore said to be 'fissile' and we use the expression 'nuclear fission'. Meanwhile, like all radioactive isotopes, they decay.
Answer:

Explanation:
In a single-displacement reaction, one element exchanges partners with another element in a compound.

This is a single-displacement reaction, because the element Fe exchanges partners with H in HCl.

This is not a single-displacement reaction, because it is a reaction between two compounds.
This is a double displacement reaction in which the K⁺ and H⁺ cations change partners with the anions.

This is not a single-displacement reaction. It is another double displacement reaction, in which the Na⁺ and H⁺ cations change partners with the anions.

This is a single-displacement reaction, because the element Ca exchanges partners with H in H₂O.
are not single-displacement reactions.
Covalent compound as it is a bond between two non-metals
In a salt solution, the water potential is lower than that in the cell. In this case, water molecules will flow from a region of higher water potential to a region of lower water potential by osmosis. Which where water molecules is now flowing out of the cell to the salt solution. Because the cell lose so much water that it now shrinks.
Osmosis is where water molecules move down the water potential gradient through a semi permeable membrane, which is the cell membrane in this case.
the time for one orbit of earth around the sun