Answer:
They are a base and an acid, so they neutralize each other.
Explanation:
Sodium hydroxide is a strong base. Hydrochloric acid is a strong acid.
They react with (neutralize) each other to form a salt (sodium chloride) and water.
NaOH + HCl ⟶ NaCl + H₂O
Answer is: Block 2 is the least dense.
d(metal) = m(metal) ÷ V(metal).
Volume is the same for all metals, so density only depends on mass of the block of the metal.
Smaller the mass of the block, smaller is the density:
d(block 1) = m(block 1) ÷ V.
d(block 1) = 65 g/V.
d(block 2) = 32 g/V.
d(block 3) = 100 g/V.
d(block 4) = 79 g/V.