Answer:
The frequency of wave is 0.125 Hz.
Explanation:
Frequency:
"It is an event repeat itself in a given period of time"
The unit of frequency is the Hz . If time is measured in seconds then frequency will be in Hz. Hz is equal to the per second.
Formula:
f = 1/ T
f = 1/ 8 sec
f = 0.125 Hz
Wave speed = frequency x wavelength
= 100 x 0.3
= 30 m/s.
Hope this helps!
Answer: The nuclide symbol of X is 
Explanation:
The given nuclear reaction is a type of alpha decay process. In this process, the nucleus decays by releasing an alpha particle. The mass number of the nucleus is reduced by 4 units and atomic number is also decreased by 2 units. The particle released is a helium nucleus.
The general equation representing alpha decay process is:

For the given equation :

As the atomic number and mass number must be equal on both sides of the nuclear equation:

Thus the nuclide symbol of X is 
Explanation:
The molarity of a solution is defined like the number of moles of solute per liters of solution.
molarity = moles of solute/(volume of solution in L)
We know the volume of solution in L.
volume of solution = 0.65 L
To go from the mass of our solute in grams to moles we have to use its molar mass.
mass of NaCl = 63 g
molar mass of NaCl = 58.44 g/mol
moles of NaCl = 63 g * 1 mol/(58.44 g)
moles of NaCl = 1.078 moles
Finally we can find the molarity of the solution
molarity = moles of NaCl/(volume of solution)
molarity = 1.078 moles/(0.65 L)
molarity = 1.66 M
Answer: the molarity of the solution is 1.66 M.