Alpha rays are: MCQ with Answer and Explanation

Explanation:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑. Carbon dioxide turns limewater milky. This is a test for carbonates and bicarbonates. The reaction is used in laboratory preparation of CO₂.

Explanation:
Rutherford's experiment led to the nuclear model of the atom, concluding that almost all the mass and positive charge are concentrated in a very small central nucleus, while electrons orbit around it. Option B is Thomson's model, A is Bohr's model, and D is de Broglie's concept.

Explanation:
Chemical properties describe a substance's ability to undergo chemical changes—reactivity with acid, flammability, oxidation states, etc. Melting point, density, boiling point are physical properties that can be observed without changing composition. Reactivity with acid involves formation of new substances. A piece of magnesium reacting with HCl is a chemical change.