How can you explain why greasy substances are difficult to wash off?

It's hard to wash off with water because water molecules are more attracted to one another than they are to oil.

Explanation:

Oil molecules are large and awkward, and they don't have poles — ends with different electric charges — so they're not very easy to bond with.

answer: -

reaction:

na + cl ⇌ nacl

balanced chemical equation:

na + 2cl ⇌ nacl2

sodium + clorine goes to form sodium chloride (table salt).

the product is nacl2.

and the reactants are na and cl.

(note: if you don’t know what ⇌ means, read below: -

⇌(double head arrow) means reversible reaction).

there is none because earth is stationary and flat.