The monomer used in the preparation of Teflon is ____________.
Teflon, a well-known polymer, is produced through the polymerization process of tetrafluoroethene \( (C_2F_4) \).
This reaction can be described by: \[ n \, F_2C=CF_2 \quad \xrightarrow{\text{polymerization}} \quad [ -CF_2-CF_2]_n \]
Therefore, the correct answer is (d) tetrafluoroethene.
Explain the construction of a spherical wavefront by using Huygens' principle.
The slope of the tangent to the curve \( x = \sin\theta \) and \( y = \cos 2\theta \) at \( \theta = \frac{\pi}{6} \) is ___________.