Question

How many electrons, protons and neutrons are present in Y\(^+\), if atomic number of Y is 19 and mass number of Y is 39 :

• A. E = 19, P = 19, N = 20
• B. E = 18, P = 19, N = 20
• C. E = 18, P = 19, N = 19
• D. E = 19, P = 20, N = 20

Hint:

Given for Y: Atomic number = 19, Mass number = 39. We need info for ion Y\(^+\). 1. {Protons (P):} Equal to atomic number. P = 19. 2. {Neutrons (N):} Mass number - Protons. N = \(39 - 19 = 20\). 3. {Electrons (E) in neutral Y atom:} Equal to protons. Neutral Y has 19 electrons. 4. {Electrons (E) in Y\(^+\) ion:} Y\(^+\) means the atom has lost 1 electron. E for Y\(^+\) = (Electrons in neutral Y) - 1 = \(19 - 1 = 18\). So, for Y\(^+\): E=18, P=19, N=20.

Answer 1

The Correct Option is B

Concept:
Atomic Number (Z) = Number of protons (P).
Mass Number (A) = Number of protons (P) + Number of neutrons (N).
For a neutral atom, Number of electrons (E) = Number of protons (P).
For an ion, the number of electrons changes:
Positive ion (cation, like Y\(^+\)): Formed by losing electrons. E = P - (charge).
Negative ion (anion): Formed by gaining electrons. E = P + |charge|. Step 1: Identify given information for element Y
Atomic number of Y (Z) = 19.
Mass number of Y (A) = 39.
We are interested in the ion Y\(^+\). Step 2: Determine the number of protons (P) The atomic number is equal to the number of protons. P = Z = 19. (The element with Z=19 is Potassium, K). Step 3: Determine the number of neutrons (N) Mass Number (A) = Protons (P) + Neutrons (N). So, Neutrons (N) = Mass Number (A) - Protons (P). N = \(39 - 19 = 20\). Number of neutrons = 20. Step 4: Determine the number of electrons (E) in the ion Y\(^+\) First, consider a neutral atom of Y. In a neutral atom, Number of electrons = Number of protons = 19. The ion is Y\(^+\), which means it has a charge of +1. A positive charge indicates that the atom has lost one electron. Number of electrons in Y\(^+\) = (Number of electrons in neutral Y) - (Number of electrons lost) Number of electrons in Y\(^+\) = \(19 - 1 = 18\). Step 5: Summarize the results for Y\(^+\)
Electrons (E) = 18
Protons (P) = 19
Neutrons (N) = 20 This matches option (2). (Option (1) E=19, P=19, N=20 would be correct for a neutral atom Y, not the ion Y\(^+\)).