Some Basic Concepts Of Chemistry JEE Main Chemistry: Authentic Shift PYQs (2021-2026) with 2.5-Min Shortcut Tricks & Trap Defense

Correct Answer: 15

Explanation: ​$M o l e \text{ } o f \text{ } \left(N a\right)^{+} = \frac{0.69}{23} = 3 \times 1 0^{- 2}$​​ ​$N a^{+} + H_{2} O \rightarrow N a O H + \frac{1}{2} H_{2}$​​ ​By using POAC ​Moles of NaOH = 3 × 10<$^{-2}$ ​NaOH reacts with HCl No. of equivalents of NaOH = No. of equivalents of HCl ​$3 \times 1 0^{- 2} \times 1 = \frac{73}{36.5} \times V \left(\text{ } i n \text{ } L\right) \times 1$​​ ​V = 1.5 × 10<$^{–2}$ L ​Volume of HCl = 15ml.​

Correct Answer: c

Explanation: ​2.40 × 10$^{23}$​ ​Number of atoms present in one mole of gas Þ 6.023 × 10$^{23}$ given (gas in diatomic → 2 atoms present in one mole) ​Thus, number of atoms Þ 6.023 × 10$^{23}$ × 2 Þ 12.046 × 10$^{23}$ No. of atoms present in 0.2 mole of gas ​= 12.046 × 0.2 × 10$^{23}$ ​= 2.40 × 10$^{23}$ atoms ​

Correct Answer: c

Explanation: Statement I is true but II is false. CH$_{4}$ + 2O$_{2}$  →  CO$_{2}$ + 2H$_{2}$O 16 g methane gives 36 g of water.

Correct Answer: c

Explanation: The element X could have an atomic weight of 7 and its oxide is X$_{2}$O Given, 14 g of element X combines with 16 g of oxygen. We know, ​​​$N u m b e r \&\text{nbsp}; o f \&\text{nbsp}; m o l e s \text{ } = \frac{\text{ } g i v e n \&\text{nbsp}; w e i g h t \text{ }}{\text{ } m o l e c u l a r \&\text{nbsp}; w e i g h t \text{ }}$​ If element X has atomic weight 7, then Number of moles of element $X = \frac{14}{7} = 2$​​ Number of moles of oxygen $O = \frac{16}{16} = 1$​ Thus, formula of oxide = X<$_{2}$O​

Correct Answer: (a)

Explanation: Detailed pedagogical breakdown based on official NCERT syllabus criteria.