Slowest to fastest
Solid, liquid, gas
A gas, HCl is a simple covalent structure which has little intermolecular attraction so this is easily overcome (pretty much the same reasons as the other one I just answered for you)
Polonium has an atomic number of 84 meaning it has 84 protons. Usually, this means there would also be 84 electrons in a normal element. A -3 charge means that there are 3 more negative electrons that positive protons so the overall number of electrons would be 87.
Lead can be extremely poisonous and was once used in many many paints but caused several deaths from lead poisoning so that was a biggie...
At the center of every chlorophyll molecule, in every plant, there is a magnesium ion. Magnesium is one of the two dozen or so elements that are <em>required </em>for life.
Below is the list of enthalpies of formation of the compounds involved in the chemical reaction.
HCl: -92.3 kJ/mol
H2: 0
Cl2: 0
Both H2 and Cl2 do not have enthaply of formation because they are pure substances.
Since, in the reaction there are 2 moles of HCl,
Enthalphy of formation = enthalpy of products - enthalphy of reactant/s
= 0 - (-92.3)(2) = +184.6 kJ
Hence, the answer is the first choice.