The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. which of the following elements would be an isotope of calcium?
1. an atom with 20 protons, 21 neutrons, and 20 electrons
2. an atom with 21 protons, 21 neutrons, and 21 electrons
3. an atom with 21 protons, 20 neutrons, and 21 electrons
4. an atom with 20 protons, 20 neutrons, and 18 electrons
5. all of the listed responses are correct.

Answer : The correct option is, (1) an atom with 20 protons, 21 neutrons, and 20 electrons.

Explanation :

Isotope : It is defined as the element that have the same number of protons but have the different number of neutrons of each of the atom.

Atomic number is defined as the number of protons or number of electrons.

Atomic number of = number of protons = number of electrons

Mass number is defined as the sum of number of protons and number of neutrons.

Number of neutrons = Mass number - Number of protons

As we are given,

Element = Calcium

Number of protons = 20

Number of electrons = 20

Number of neutrons = 20

For the isotope of calcium, the element should have the same number of protons but the different number of neutrons of each of the atom.

From this we conclude that, the option (1) would be an isotope of calcium because in this the protons and electrons are same but neutrons are different.

Hence, the correct option is, (1) an atom with 20 protons, 21 neutrons, and 20 electrons.

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step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.