Which of the four atoms P,Q,R, and S in the above data can be described by the following properties: relative atomic mass is greater than 30 but less than 40; it has an odd atomic number and forms a unipositive ion in solution?

Which of the four atoms P,Q,R, and S in the above data can be described by the following properties: relative atomic mass is greater than 30 but less than 40; it has an odd atomic number and forms a unipositive ion in solution?

                                 P      Q      R        S

Proton                      13    16     17      19

Electron                   13    16     17      19

Neutron                   14    16     35      20

A. P

B. Q

C. R

D. S

Correct answer is D

Explanation

First, calculate the relative atomic mass (mass number) of each atom:

Mass number = protons + neutrons

• P: 13 + 14 = 27 ❌ (less than 30)

• Q: 16 + 16 = 32 ✅

• R: 17 + 35 = 52 ❌ (greater than 40)

• S: 19 + 20 = 39 ✅

Now apply the other conditions:

1. Relative atomic mass > 30 but < 40

✔ Q (32), ✔ S (39)

2. Odd atomic number

• Q: atomic number = 16 (even) ❌

• S: atomic number = 19 (odd) ✅

3. Forms a unipositive ion in solution

Atomic number 19 corresponds to potassium (K), which forms K⁺ (a unipositive ion) ✅

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✅ Correct Answer: D. S

Number Nine