An atom of an unknown element contains 17 protons and 19 neutrons. The total number of electrons present in a neutral atom of this element is

This isotope of fluorine has 9 protons, 9 electrons and 10 neutrons.

Explanation:

The atomic number is the number of protons  ( p + ) . In a neutral atom, the number of electrons  ( e − )  equals the number of protons. Mass number is the sum of the protons and neutrons  ( n 0 )  of a particular isotope. If you have mass number and atomic number, subtract the atomic number from the mass number to get the number of neutrons.  ( Mass number ) − ( atomic number ) = number of neutrons .

There are:

9 protons

9 electrons

10 neutrons

Fluorine is the element in question, as its atomic number is  9 . You would name this particular isotope using the mass number. It would be called fluorine-19.

The nuclear or isotopic notation would be  19 9 F

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).