Unbalancing Wheatstone Bridge for Positive Voltmeter Reading Steps: - Assume a balanced Wheatstone bridge with four 1kΩ arms (two fixed resistors, thermistor, LDR), voltmeter across bridge points X and Y, initially reading 0V as V_X = V_Y. - Positive reading requires V_X > V_Y, achieved by increasing resistance in the arm connected to Y or decreasing in the arm to X. - Evaluate each option's effect on bridge balance. - Determine which solely causes the desired unbalance. Why C is correct: - LDR resistance decreases with increased light intensity (photoconductive effect); if LDR is in the arm raising V_X, this lowers its resistance, increasing V_X relative to V_Y for positive reading. Why the others are wrong: - A: Decreasing voltmeter resistance adds loading but does not alter bridge potentials, so reading stays near 0V. - B: Decreasing thermistor temperature increases its resistance (NTC behavior), but depending on position, it may unbalance oppositely or not cause V_X > V_Y. - D: Replacing fixed resistor with 500Ω decreases resistance, unbalancing bridge but likely lowers V_X if in the relevant arm, yielding negative …