Question

What is half-life of a radioactive element?

The time taken for the parent element to disappear.

The time taken for half of the original number of nuclei to decay

The time taken for the volume of a sample to reduce to half its original value

The time taken for the mass of a sample to reduce to half its original value.

The number of electrons in a normal atom is the same as:

(i)    the number of protons in its nucleus

(ii)   the atomic number of the element the atom belongs to

(iii)   the number of neutrons in the nucleus

(i) only

(i) and (ii) only

(ii) and (iii) only

(iii) ony

For an electron in an atom to change from the ground state to an excited state:

Group of answer choices

energy must be absorbed

radiation must be emittd

the nucleus need to release energy

energy must be released

According to quantum mechanical model, a three dimensional region around the nucleus where an electron may be found is called:

Group of answer choices

a spectralline

an orbital

an energy level

an electron path

The atominc number of an element is Z = 29. If there are 32 neutrons in the nucleus, what is the mass number of the element?

29

61

55

32

Bohr's model of the atom helped explain why

Group of answer choices

atoms combine to form molecules

electrons have negative charge

most of the mass of the atom is in the nucleus

excited hydrogen gas give off certain colors of light.

What are alpha particles?

Group of answer choices

Alpha particles are electrons

Alpha particles are atoms of helium

Apha particles are heium nuclei consisting of two protons and 2 neutrons

Alpha particles consists of protons

Need help with these please.

Answer 1

1. number of neutron is not necessarily equal to the number of electrons in a normal atom. So the number of electron will be equal to number of proton in the nucleus and also to the atomic number. Hence correct option is (i) and (ii) only.

2. Mass number of an element = Number of proton (atomic number) + number of neutron. In this case, Mass number =29+32= 61. Hence correct option is 61.

3. Alpha particle is He^{​​​​​2+} , which contains zero electron, 2 proton , 2 neutron. So the correct answer is Alpha particles are atoms of Helium nuclei consisting of two proton and 2 neutron.

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