Answer:
Mendeleev had left the noble gases out of his periodic table.
Explanation:
Mendeleev's periodic table is pictured in the image attached to the question.
Mendeleev's table obviously lacked the noble gases. The reason for this grave omission is simple; the noble gases were not known as at the time when he formulated his periodic table. There weren't any known elements whose properties were similar to the properties of the noble gases. This would have lead him to suspect their existence.
Answer:
Helium
Explanation: The ionization energy decreases from the top to bottom in groups. And increases from left to the right across a period. Therefor Helium has tge largest first ionization energy, while francium has one of the lowest.
The answer is "night sky"
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In a 0.01 M solution of HCl, Litmus will be red. Litmus paper will turn into red in acidic conditions. Hydrochloric acid is an acid. Litmus is an indicator for acidity and alkalinity made from inchens.
