The greatest evolutionary change enabling land vertebrates to be completely free from water habitats was the development of:

Five elements $A, B, C, D$ and $E$ have work functions $1.2\, eV, 2.4\, eV, 3.6\, eV, 4.8\, eV$ and $6\, eV$ respectively. If light of wavelength $4000\, \mathring{A}$ is allowed to fall on these elements,then photoelectrons are emitted by

The length of an elastic string is $a$ metres when the longitudinal tension is $4 \ N$ and $b$ metres when the longitudinal tension is $5 \ N$. The length of the string in metres when the longitudinal tension is $9 \ N$ is

$50 \Omega$ and $100 \Omega$ resistors are connected in series. This combination is connected to a battery of $2.4 \text{ V}$. When a voltmeter of $100 \Omega$ resistance is connected across the $100 \Omega$ resistor,the reading of the voltmeter will be .......... $\text{V}$.

$A$ cannon ball is fired with a velocity $200\, m/s$ at an angle of $60^{\circ}$ with the horizontal. At the highest point of its flight,it explodes into $3$ equal fragments. One fragment goes vertically upwards with a velocity $100\, m/s$,and the second one falls vertically downwards with a velocity $100\, m/s$. What will be the velocity of the third fragment?

The incentre of the triangle formed by the lines $x+y=1$,$x=1$,and $y=1$ is