The magnetic field of the earth can be modelled by that of a point dipole placed at the centre of the earth. The dipole axis makes an angle of 11.3° with the axis of the earth. At Mumbai, declination is nearly zero. Then, [NCERT Exemplar]

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declination averaged over the earth must be always negative

the least declination is 0⁰

the declination varies between 11.3⁰W to 11.3⁰E

the plane defined by dipole axis and the earth axis passes through Greenwich

answer is A.

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Detailed Solution

For the earth's magnetism, the magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth.
The axis of the dipole does not coincide with the axis of rotation of the earth but is presently tilted by approximately 11.3⁰ with respect to the later. This results into two situations as given in the figures below