X-ray tube targets are made of tungsten due to its high melting point and efficiency in producing X-rays; OCR shows Tungsten marked.

Blue-dominated spectra indicate higher surface temperature, red indicates lower, and yellow is intermediate, so B hottest, A coolest, C intermediate.

Bones are denser and absorb more X-rays, so fewer X-rays reach the film behind bones, making those areas lighter.

The observed change in frequency (redshift/blueshift) is due to relative motion between the source and observer (Doppler effect); the OCR marks option B.

Audio waves are mechanical (pressure) waves in a medium, not electromagnetic waves.

Microwave ovens commonly use a frequency of about 2450 MHz, therefore option B is correct.

Wilhelm Roentgen discovered X-rays in 1895 and is credited with their discovery.

Number of emitted electrons is proportional to the number of incident photons, i.e., the light intensity, not the photon energy or work function.

In electromagnetic waves both electric and magnetic fields oscillate (vary) in time and space.

Radiowaves possess the lowest frequencies and hence the lowest photon energies in the electromagnetic spectrum.