The d subshell can hold up to 10 electrons in an atom. true false

TRUE

Explanation:

Each electronic shell in an atom is composed of subshells, which are denoted by the symbol s, p, d and f. These subshells are represented by the principal quantum number (n) and the azimuthal quantum number (ℓ).  

Each subshell can hold a fixed number of electrons, which is equal to (4ℓ + 2) electrons.

For, d subshell the value of ℓ = 2.

Therefore, the maximum number of electrons that a d-orbital can hold = (4ℓ + 2) electrons = (4×2 + 2) electrons = 10 electrons.

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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.