Which of the following pairs of orbitals possess two nodal planes?

$\int_0^\pi \frac{1}{1+\sin x} \, dx$ is equal to

If one of the lines represented by $ax^2+2hxy+by^2=0$ passes through $(2,3)$ and the other passes through $(4,5)$,then $a+2h+b$ equals

The value of ${\log _3}4 \times {\log _4}5 \times {\log _5}6 \times {\log _6}7 \times {\log _7}8 \times {\log _8}9$ is:

Two rods of different materials having coefficients of linear expansion $\alpha_1$ and $\alpha_2$ and Young's moduli $Y_1$ and $Y_2$ respectively are fixed between two rigid massive walls. The rods are heated such that they undergo the same increase in temperature. There is no bending of rods. If $\alpha_1 : \alpha_2 = 2 : 3$,the thermal stress developed in the two rods is equal provided $Y_1 : Y_2$ is equal to:

$A$ horizontal force of $10\,N$ is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and wall is $0.2$. The weight of the block is ........ $N$.