In which plant group are the sporophylls arranged spirally along an axis to form distinct compact structures called strobili or cones?

In order to double the frequency of the fundamental note emitted by a stretched string,the length is reduced to $\frac{3}{4}$ of the original length and the tension is changed. The factor by which the tension is to be changed is

Given that $a, b \in \{0, 1, 2, \ldots, 9\}$ with $a+b \neq 0$ and that $\left(a+\frac{b}{10}\right)^x = \left(\frac{a}{10}+\frac{b}{100}\right)^y = 1000$. Then,$\frac{1}{x}-\frac{1}{y}$ is equal to

The angle of incidence at which reflected light is totally polarized for reflection from air to glass (refractive index $n$) is

Who first discovered lichens?

The $pH$ of the solution containing $10 \ mL$ of $0.1 \ N \ NaOH$ and $10 \ mL$ of $0.05 \ N \ H_2SO_4$ would be: