Complete Question
The complete question is shown on the first uploaded image
Answer:
The bond angle is 104.48⁰
Explanation:
The explanation is shown on the second uploaded image
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: protons and neutrons.
The nucleus is made up of 3 subatomic particles that are protons,neutrons and electrons.
General notation of an element is 
where, X is the Element, A is the Atomic Mass and Z is the Atomic Number
If we know the number of protons we can easily find out the atomic number of any element because Atomic Number = Number of protons in an element.
And in addition if we know the number of neutrons we can easily find out the atomic mass of an element because
Atomic Mass = (Number of protons) + (Number of neutrons)
If we get to know the atomic number and atomic mass, we can easily tell what element is it by looking from the periodic table.
HCN is a Bronsted acid; it can dissociate into H+ and CN-. And H+ is a Lewis acid because it accepts election pairs. ... In order for H+ and CN- to be formed, Hydrogen in HCN donates its electrons to Carbon. So in this sense, Hydrogen is the lewis base and Carbon is the lewis acid.