Answer:
Q2->They all form acids when combined with hydrogen. They are all fairly toxic. They readily combine with metals to form salts.
Q3->Because their outermost orbit is complete. In Mendeleev's original periodic table there was no place reserved for noble gas. They were discovered in end of 19th century. So Mendeleev created zero group without disturbing original periodic table.
Explanation:
The Englishman Robert Hooke (18th July 1635 - 3rd March 1703) was an architect, natural philosopher and brilliant scientist, best known for his law of elasticity (Hooke's law), his book Micrographia, published in 1665 and for first applying the word "cell" to describe the basic unit of life. It is also less well known that there is substantial evidence that Hooke developed the spring watch escapement, independently of and some fifteen years before Huygens, who is credited for this invention. Hooke also is recognised for his work on gravity, and his work as an architect and surveyor.
Hooke's Micrographia
Here, we focus on his pioneering work using the microscope to document observations of a variety of samples in his book Micrographia, published in September 1665.
Hooke began his famed career by initially studying at Wadham College, Oxford, where he worked closely under John Wilkins with other contemporaries, including Thomas Willis and Robert Boyle, for whom he built the vacuum pumps used in Boyle's gas law experiments. He also built some of the earliest telescopes, observing the rotations of Mars and Jupiter, and, based on his observations of fossils, was an early proponent of biological evolution. If that wasn't enough, he investigated the phenomenon of refraction, deducing the wave theory of light, and was the first to suggest that matter expands when heated and that air is made of small particles separated by relatively large distances, yet curiously Robert Hooke is somewhat overlooked in his contributions to science, perhaps as there were many people who wrote of Hooke as a difficult personality, being described as of "cynical temperament" and of "caustic tongue". There were also disputes with fellow scientists, including disputes with Isaac Newton over credit for work on gravitation and the planets. Though it must be remembered that Hooke lived at a time of immense scientific progress and discovery and none of the above diminish Hooke'
