(2) Cr is the correct answer.

Table J, the activity series, presents a list of metals from most active to least active.  You can see that Cr falls between Ni and Zn on this table.

(1) alpha particle is the correct answer.

Alpha particles are made of 2 protons and 2 neutrons. This means that they have a charge of +2, and a mass of 4 (the mass is measured in "atomic mass units", where each proton and neutron=1)

Beta particles have a charge of minus 1, and a mass of about 1/2000th of a proton. This means that beta particles are the same as an electron.

Gamma rays are waves, not particles.  This means that they have no mass and no charge.

Positrons are positively charged electrons which mean they have the same mass as an electron.

1) is the correct answer.

According to Table N Selected Radioisotopes, Calcium-37 and Iron-53 both use Beta Positive decay.

(1) alpha particle, beta particle, gamma ray is the correct answer.

Alpha particles have the lowest penetrating power, as they can be stopped by even a sheet of paper.  Beta particles are a bit more powerful, they can be stopped by lead.  Gamma rays are waves which can be stopped, but by thick concrete or lead.

(4) production of energy.Nuclear fission reactions are used to produce energy in nuclear power plants.  Unfortunately, the waste products of these reactions break down slowly and must be stored.  Living organisms exposed to nuclear radiation can suffer negative consequences.

(4) 1/32 is the correct answer.

If we refer to Table N, we can see that nitrogen-16 has a half-life of 7.2 seconds.

After 7.2 seconds, there are 10 grams remaining.

After 14.4 seconds, there are 5 grams remaining.

After 21.6 seconds, there are 2.5 grams.

After 28.8 seconds, there are 1.25 grams remaining.

After 36 seconds, there are .75 grams remaining.

.75/20 = .0375 = 1/32

(2) Cobalt-60 is the correct answer.

Carbon 14 is used in carbon dating.  Lead is a poisonous metal so would not be a good choice for human use.  Uranium 238 is used to craft nuclear weapons.