Answer:
The correct answer is option b.
Explanation:

The ionic product of water : 
![K_w=[H^+][OH^-]](https://tex.z-dn.net/?f=K_w%3D%5BH%5E%2B%5D%5BOH%5E-%5D)
A pure water has equal concentration of hydrogen ions and hydroxide ions, hence neutral.
![K_w=[H^+][H^+]=[H^+]^2](https://tex.z-dn.net/?f=K_w%3D%5BH%5E%2B%5D%5BH%5E%2B%5D%3D%5BH%5E%2B%5D%5E2)
The ionic product of water at 283 K = 
![K_w=[H^+]^2](https://tex.z-dn.net/?f=K_w%3D%5BH%5E%2B%5D%5E2)
![0.29\times 10^{-14}=[H^+]^2](https://tex.z-dn.net/?f=0.29%5Ctimes%2010%5E%7B-14%7D%3D%5BH%5E%2B%5D%5E2)
![[H^+]=5.385\times 10^{-8} M](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D5.385%5Ctimes%2010%5E%7B-8%7D%20M)
The pH of the water at 283 k;
![pH=-\log [H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%20%5BH%5E%2B%5D)
![=-\log[5.385\times 10^{-8} M]=7.26](https://tex.z-dn.net/?f=%3D-%5Clog%5B5.385%5Ctimes%2010%5E%7B-8%7D%20M%5D%3D7.26)
A pure water has equal concentration of hydrogen ions and hydroxide ions,So water will e neutral at this temperature also.
The correct answer is option b.
7 - Neutral because water and salt are neutral substances
For waves velocity (v) is equal to the wavelength (λ) times frequency (f). (They are inversely proportional)
V=λf
Since V is constant, if frequency increases, wavelength decreases.
Answer:
This is because of diffusion , the movement of particles from an area of high concentration to an area of low concentration. ... This means that diffusion does not happen in solids – the particles in a solid can only vibrate and cannot move from place to place.