Which one of the following compounds forms a quaternary salt on reacting with excess methyl iodide?

In which of the following reactions is the product an ether?

If an electron in a hydrogen atom jumps from the $3^{\text{rd}}$ orbit to the $2^{\text{nd}}$ orbit,it emits a photon of wavelength $\lambda$. When it jumps from the $4^{\text{th}}$ orbit to the $3^{\text{rd}}$ orbit,the corresponding wavelength of the photon will be

Knowing the properties of $H_{2}O$ and $D_{2}O$,do you think that $D_{2}O$ can be used for drinking purposes?

Hydrolysis of sucrose with dilute aqueous sulphuric acid yields

The second maturation division of the mammalian ovum occurs: