The correct answer is Option (4) → (A), (C) and (D) only
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(A) The bridge is most sensitive when all the four resistances are of the same order: This is correct. When the resistances P,Q,R, and S are roughly equal or of the same order of magnitude, the galvanometer shows a more detectable deflection for a small change in the unknown resistance, making the bridge highly sensitive.
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(B) The internal resistance of the cell and the resistance of the galvanometer affect the null point: This is incorrect. At the null point (balanced condition), no current flows through the galvanometer. Therefore, the value of the galvanometer's resistance (G) or the internal resistance of the battery does not shift the position of the null point. They only affect the sensitivity of the bridge (how quickly the needle moves), not the position of balance.
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(C) It does not involve measurement of current and potential difference: This is correct. A Wheatstone bridge is a null-method device. It relies on finding a state where the current through the galvanometer is zero. We compare known resistances to find an unknown one (Rx​=R2​⋅R3​/R1​), rather than reading values from a scale of Volts or Amperes.
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(D) Resistances of ammeters and voltmeters do not affect the measurements: This is correct. Since the measurement is based on a null deflection (zero current) in the middle branch, and we are not using ammeters or voltmeters to determine the resistance value, their presence or internal resistances do not influence the accuracy of the balanced bridge.
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