In a moving-coil instrument , the coil is suspended in a radial magnetic field instead of a uniform magnetic field . This is done to :

Increase the sensitivity of the instrument

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increases the accuracy of the instrument

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make the instrument compact and protable

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make its deflection proportinal to current through it

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Solution

The correct option is B increases the accuracy of the instrument
The horseshoe magnet has cylindrically concave pole-pieces. Due to this shape, the magnet produces a radial magnetic field so that when coil rotates in any position its plane is always parallel to the direction of the magnetic field. When current flows through the coil it gets deflected.
Hence, increases the accuracy of the instrument

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