The correct answer is (a) Weber.
A weber (Wb) is the SI unit of magnetic flux. It is named after Wilhelm Weber, a German physicist and mathematician.
Magnetic flux is the measure of the total magnetic field passing through a surface. It is calculated by multiplying the magnetic field strength, B, by the area, A, of the surface.
The magnetic field strength is a vector quantity that describes the strength and direction of a magnetic field. It is measured in teslas (T).
The area is a scalar quantity that describes the size of a surface. It is measured in square meters (m2).
The SI unit of magnetic flux is the weber (Wb). One weber is equal to the magnetic flux through a surface of one square meter when the magnetic field strength is one tesla.
The other options are not correct.
(b) Gauss is the CGS unit of magnetic flux density. It is named after Carl Friedrich Gauss, a German mathematician and physicist.
(c) Amp./meter is the SI unit of magnetic field strength. It is also called the ampere-turn per meter.
(d) Oersted is the CGS unit of magnetic field strength. It is named after Hans Christian Ãrsted, a Danish physicist and chemist.