Why are metals so strong and hard ?​

Metals are tough because of an effect called plasticity

Explanation:

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https://en.wikibooks.org/wiki/A-level_Physics_(Advancing_Physics)/Metals#:~:text=Metals%20are%20tough%20for%20the,This%20effect%20is%20called%20plasticity.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.

answer; the numbers of valence electrons in the acetic acid molecule (ch3co2h) is 24;