1) As the elements in Period 2 of the Periodic Table are considered in order from left
to right, which property generally decreases?

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

it would be b. 6co2 + 6h2o --> c6h12o6 + 6o2