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The value closest to the thermal velocity of a Helium atom at room temperature (300 K) in m s⁻¹ is [k_B=1.4 × 10⁻²³ J/K; m_He=7 × 10⁻²⁷ kg]

Asked in JEE Main 2018 · Speed with temperature and molar mass

• (1) 1.3 × 10³
• (2) 1.3 × 10⁵
• (3) 1.3 × 10²
• (4) 1.3 × 10⁴

Step-by-step solution

Why the other options are wrong

• (2) Two decades too large, from a slip in the exponent of the mass.
• (3) A decade too small, from reading √1.8×10⁶ as 1.3×10².
• (4) A decade too large, from using m=7×10⁻²⁹ kg.

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