SSC CGL Science – Matter & Atomic Structure – Level 3 · Challenge

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SSC CGL Science – Matter & Atomic Structure – Level 3 · Challenge – 8 questions, subject: General Science. Every question has the correct answer with a one-line explanation; tap "Show Answer". Free practice for TNPSC, UPSC, SSC, Bank and RRB exams – Shanmugam IAS Academy, Coimbatore.

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1.  
An element has two isotopes of mass 10 u (20%) and 11 u (80%). Its average atomic mass is:

Correct Answer: B [10.8 u]

Explanation:

(10 × 20 + 11 × 80) ÷ 100 = 1,080 ÷ 100 = 10.8 u.

2.  
An ion X²⁺ has 18 electrons. The atomic number of X is:

Correct Answer: B [20]

Explanation:

Z = electrons + charge = 18 + 2 = 20 (calcium).

3.  
Statement-basedWhich of these are features of Rutherford's model of the atom?
I. A small, dense, positively charged nucleus.
II. Electrons revolve around the nucleus.
III. It explained the stability of the atom.

Correct Answer: D [Only I and II]

Explanation:

Rutherford's model could NOT explain stability – Bohr's model addressed that.

4.  
The total number of atoms in 0.5 mol of ammonia (NH₃) is:

Correct Answer: A [1.2044 × 10²⁴]

Explanation:

0.5 mol molecules × 4 atoms each = 2 mol atoms = 2 × 6.022 × 10²³.

5.  
Match the followingMatch the mixture with the method:
P. Ammonium chloride + salt Q. Oil + water R. Dyes in black ink S. Acetone + water
1. Separating funnel 2. Sublimation 3. Distillation 4. Chromatography

Correct Answer: C [P-2, Q-1, R-4, S-3]

Explanation:

NH₄Cl sublimes; oil–water immiscible; dyes move at different speeds; acetone boils much lower than water.

6.  
An element with atomic number 15 has how many valence electrons, and what valency does it show in its hydride (PH₃)?

Correct Answer: C [5 and 3]

Explanation:

2, 8, 5 → 5 outer electrons; with hydrogen it needs 3 more → valency 3 in PH₃ (it shows 5 in P₂O₅).

7.  
Which atom is an isotone of ¹³C (Z = 6)?

Correct Answer: D [¹⁴N (Z = 7)]

Explanation:

¹³C has 13 − 6 = 7 neutrons; ¹⁴N has 14 − 7 = 7.

8.  
Statement-basedWhich one of the following statements is NOT correct?

Correct Answer: B [Isobars have the same number of protons]

Explanation:

Isobars share the mass number but have different atomic numbers (protons).

➤ Full notes, shortcuts and every answer explained – SSC CGL 2026 General Science book (₹149): www.shanmugamiasacademy.in/study-materials/ssc-cgl-general-science

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