In an electron-dot symbol of an element, the dots are used to represent .

Valence electrons.

Explanation:

Hello,

In this case, the electron dot structure is widely known for representing the valence electrons as dots placed around the chemical symbol and they are defined as the electrons configured at the outermost shell of the studied atom. Commonly, electrons are placed up to two on each side of the elemental symbol for a maximum of eight. For instance, sodium has one valence electron, sulfur has six valence electrons, helium has eight valence electrons and so on. Valence electrons are known to be dependent of the electron configuration.

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"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"

the answer is a! (2.9 x 10^-18 j) hope i could someone. : )