What evidence of a chemical reaction might you see dropping an alka seltzer

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

Not a  mixture of two common elements that can be separated by physical means.

A- electron repulsion favors a tetrahedral shape, so the orbitals are 109.5° apart from each other. of a hydrogen atom on methane. they may also contain lone pairs—this explains the geometry of water, which is sp3 hybridized due to the lone pair, which occupies one of the four hybrid orbitals.

Answer: 1s²  2s²  2p⁶explanation: from the periodic table, we can note that the neutral fluorine  has 9 electrons (symbol is shown in the attached image)therefore, the configuration of neutral fluorine  is: 1s²  2s²  2p⁵now, f⁻  means that the neutral fluorine  gained one extra electron. this means that f⁻  has 10 electrons.the extra electron will occupy the 2p level to make it complete.the configuration now  is: 1s²  2s²  2p⁶comparing between both f and f⁻, we can note that f⁻  has now complete orbitals which means that it is more stable than f based on lewis postulatehope this : )