The correct answer is D. Singhbhum.
Iron ore is found in Jharkhand in the district of Singhbhum. The district is located in the eastern part of the state and is one of the most important mining districts in India. The iron ore deposits in Singhbhum are of high quality and are used to produce iron and steel.
The other options are incorrect. Lohardagga is a district in the northern part of Jharkhand. Dumka is a district in the southern part of Jharkhand. Dhanbad is a district in the central part of Jharkhand.
Lohardagga is not a major mining district. The iron ore deposits in Lohardagga are of low quality and are not used to produce iron and steel.
Dumka is not a major mining district. The iron ore deposits in Dumka are of low quality and are not used to produce iron and steel.
Dhanbad is a major mining district. The iron ore deposits in Dhanbad are of high quality and are used to produce iron and steel. However, the iron ore deposits in Dhanbad are not as good as the iron ore deposits in Singhbhum.