Ultrasound was used to check for cracks in an aeroplane wing. The ultrasound pulse would be reflected from any cracks and from the end of the wing. The diagram shows the oscilloscope trace produced by the echo. How far along the wing was the crack? The speed of sound in metal is 5000 M/S.

Your answer is c. explanation: plasma  is the fourth state of matter, derived from the gaseous state of matter.  plasma  can contain free  electrons  and/or  ions. while  plasma is never neutral, it can either be positively or negatively charged.  gases, however, are electrically neutral.

Answerthe valence of an element or radical is equal to the number of positive or negative charges on the ion.