What is the period number in which helium is found? what is the group name in which helium is found?

Period no. = 1, Group no. = 18

Explanation:

Atomic number of He = 2

Helium is placed in period 1 and group 18.

Helium is an inert gas and also known noble gas.

Helium is the first element placed in group 18.

Helium is a colourless, odder-less gas. Its outer shell (K shell) is fully occupied and so has inert gas configuration.

Because of inter gas configuration, it is chemically inactive.

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.