Which of the following ethers cannot be produced by Williamson ether synthesis?

Which of the following is the correct structure of $L$-glucose?

The total revenue in Rupees received from the sale of $x$ units of a product is given by $R(x) = 3x^2 + 36x + 5$. The marginal revenue,when $x = 15$,is

Five identical springs are used in the following three configurations. The time periods of vertical oscillations in configurations $(i)$,$(ii)$ and $(iii)$ are in the ratio:

Observe the following statements :
$I$. The physical and chemical properties of elements are periodic functions of their electronic configuration.
$II$. Electronegativity of fluorine is less than the electronegativity of chlorine.
$III$. Electropositive nature decreases from top to bottom in a group.
The correct answer is :

$A$ vertical bar magnet is dropped from a position on the axis of a fixed metallic coil as shown in fig-$I$. In fig-$II$,the magnet is fixed and a horizontal coil is dropped. If the acceleration of the magnet and the coil are $a_1$ and $a_2$ respectively,then: