Which of the following is a serious source of experimental error? a. The sodium hydroxide is not mixed completely in the Florence flask.
b. The buret is not conditioned.
c. The KHP samples are dissolved in 50 mL (not 25 mL) of distilled water.
d. Two drops (not one drop) of phenolphthalein indicator is used.
e. Bubbles are not cleared from the tip of the buret.
f. The Erlenmeyer flasks are not dry before pipetting the vinegar samples.

with this one i know the answer in craters one reason i looked it up and i learned about it there is my evidence

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

if you need further assistance, let me know: )

~ trueboss72

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8