The new element "Leo (L)" has three stable isotopes: L-82 (exact mass: 81.8735), L-85 (exact mass: 84.8322), and L-86 (exact mass: 85.6299). The relative abundances are 64.8%, 18.5%, and 16.7%, respectively. What is the average atomic
mass of element L?

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.

answer carbon and three oxygen atoms;