Question 5
What does the ⇌ sign in 3Fe + 4H2O ⇌ Fe3O4 + 4H2 tell us?
The right answer is the one marked above.
That the reaction is reversible. That is, products can form from the reactants and reactants from the products.
Reversible though it is, this remains a chemical change — new substances form. That a reaction needs heat is shown by a Δ over the arrow, not by a double head.