What is technique error and how can it be avoided?

Explanation:

Technique errors most commonly occur due to incorrect placement of the detector, wrong vertical or horizontal alignment of the X-ray beam, or collimator centering.

These errors can be avoided by placing the receptor relationship in alignment with the teeth so that the x-ray beam travels directly through the contact areas. This will place the receptor parallel to the buccal plane of the teeth of interest as well as the parallel to the instrument indicator ring.

c. 4.54 x 10–12 j happens to be correct

the answer is d. matter from the air combined with the steel wool.