During which phase of mitosis do the nuclear envelope and nucleolus completely disappear?

The solution of the differential equation $\frac{dy}{dx} = \frac{y}{x} + \frac{\phi \left( \frac{y}{x} \right)}{\phi' \left( \frac{y}{x} \right)}$ is

If the number of $5$-element subsets of the set $A = \{a_1, a_2, \ldots, a_{20}\}$ of $20$ distinct elements is $k$ times the number of $5$-element subsets containing $a_4$,then $k$ is

Acetaldehyde forms a white crystalline precipitate on mixing with a ...... solution of

The value of $a$ for which the system of equations $a^3x + (a + 1)^3y + (a + 2)^3z = 0$,$ax + (a + 1)y + (a + 2)z = 0$,$x + y + z = 0$ has a non-zero solution is

For a normal eye,the cornea of the eye provides a converging power of $40 \ D$ and the least converging power of the eye lens behind the cornea is $20 \ D$. Using this information,the distance between the retina and the cornea-eye lens can be estimated to be.......... $cm$.