Aeration is a process used in water treatment to promote the conversion of dissolved contaminants into solid particles that can be easily removed. It is particularly effective for the removal of certain dissolved metals.
Therefore, the correct answers are (A) and (C).
| Air Pollutants | Treatment techniques | ||
| P | NO2 | i | Flaring |
| Q | SO2 | ii | Cyclonic separator |
| R | CO | iii | Lime scrubbing |
| S | Particles | iv | NH3 injection |
Consider a five-digit number PQRST that has distinct digits P, Q, R, S, and T, and satisfies the following conditions:
1. \( P<Q \)
2. \( S>P>T \)
3. \( R<T \)
If integers 1 through 5 are used to construct such a number, the value of P is:



