During science lab, some students added small pieces of magnesium ribbon to 10 ml of hydrochloric acid. they noticed that bubbles formed, the test tube got hot, and the magnesium disappeared.
which is a sign that a chemical reaction has taken place in this experiment?
a) change in odor
b) change in color
c) release of heat energy
d) disappearance of magnesium

C) release of heat energy

Explanation: A chemical change is a change which is accompanied by a change in chemical composition of the atoms.

Chemical changes are accompanied by:

a) Change in color

b) Absorption or release of heat

c) formation of precipitates

d) production of gas.

Here no change in color is there, but is given that the tube gets hot, that means the energy has been released.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)