Answer:
Electromagnetic waves do not require any medium to travel whereas mechanical waves must have a medium to propagate.
So, Basically, it is B I believe.
Hope It Helps!
Answer:
Time will be 19 ms so option (a) is correct option
Explanation:
We have given that mass of wire m = 50 gram = 0.5 kg
Frequency f = 810 Hz
Wavelength = 0.4 m
Velocity is given by

Amplitude is given as d = 6 m
So time 
So option (a) is correct option
Answer: J.J Thomson
Explanation: J. J. Thomson, who discovered the electron in 1897, proposed the plum pudding model of the atom in 1904 before the discovery of the atomic nucleus in order to include the electron in the atomic model.
Usually, it increases the solubility in water.