Which missing item would complete this alpha decay reaction?

257/100 fm= +4/2he

The technique here is to balance the number of particles which is the numerator and the number of protons which is the denominator

Therefore

NUMERATOR:

257 – 4 = 253

DENOMINATOR:

100 – 2 = 98

 the number of protons of an ion is simply its atomic number therefore, from the periodic table

98 = Californium

The answer here is that we will add an Isotope of californium, 253/98 Cf

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).

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.