Which of the following is a redox reaction?

A positive ion $A$ and a negative ion $B$ has charges $6.67 \times 10^{-19}\ {C}$ and $9.6 \times 10^{-10}\ {C}$, and masses $19.2 \times 10^{-27}\ {kg}$ and $9 \times 10^{-27}\ {kg}$ respectively. At an instant, the ions are separated by a certain distance $r$. At that instant the ratio of the magnitudes of electrostatic force to gravitational force is ${P} \times 10^{-13}$, where the value of $P$ is _________ .
(Take $\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9\ {Nm}^2 {C}^{-1}$ and universal gravitational constant as $6.67 \times 10^{-11}\ {Nm}^2 {kg}^{-2}$)

Consider the reaction at $300\, K$:
$C_6H_{6(l)} + \frac{15}{2} O_{2(g)} \to 6 CO_{2(g)} + 3 H_2O_{(l)}$; $\Delta H = -3271\, kJ$
What is $\Delta U$ for the combustion of $1.5\, mol$ of benzene at $27\, ^\circ C$? .....$kJ$

When a wire of length $10 \ m$ is subjected to a force of $100 \ N$ along its length,the lateral strain produced is $0.01 \times 10^{-3} \ m$. The Poisson's ratio was found to be $0.4$. If the area of cross-section of the wire is $0.025 \ m^2$,its Young's modulus is

If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k=$

Two identical balls $A$ and $B$ are released from the positions shown in figure. They collide elastically on the horizontal portion $MN$. The ratio of the maximum height attained by $A$ and $B$ after the collision will be: (neglect friction)