Which missing item would complete this alpha decay reaction?
21CF-247 Cm +

the atomic number decreased in 2, from 100 to 100 - 2 = 98. 3) Hence the formed atom has atomic number 98, which is californium, Cf, and the isotope is californium - 253. 4) The item that completes the given alpha decay reaction is: ₉₈²⁵³ Cf.

Explanation:

20 drops hope this

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.