Which of the following is a fossil pteridophyte?

The quadratic equation whose roots are $\sin ^2 18^{\circ}$ and $\cos ^2 36^{\circ}$ is :

Consider three observations $a, b$ and $c$ such that $b = a + c$. If the standard deviation of $a + 2, b + 2, c + 2$ is $d$,then which of the following is true?

Euchlorine is a mixture of

$A$ constant volume gas thermometer shows pressure readings of $50 \, cm$ and $90 \, cm$ of mercury at $0^{\circ} C$ and $100^{\circ} C$ respectively. When the pressure reading is $60 \, cm$ of mercury,the temperature is ......... $^{\circ} C$.

When is the immune response most intense?