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5.0 mg of radioactive nobelium-253 was removed from the reactor to be
used in an experiment. It took 291 seconds (just under 5 minutes) to
get the sample from the reactor to the laboratory. How many milligrams
of nobelium-253 remained upon arrival to the laboratory? The half-life
of nobelium-253 is 97 seconds.

Explanation:

Half life of Nobelium-253 is 97 seconds . That means after every 97 seconds half of the Nobelium amount will be disintegrated .

Time taken in bringing the sample to laboratory = 291 seconds

291 second = 291 / 97 half life

n = 3

N =

N₀ is original mass , N is mass after n number of half life.

N = 5 mg x

= .625 mg

Only  0.625 mg of Nobelium-253 will be left .

1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.