Which of the following elements does not form a monoxide?

If $t_n$ denotes the number of triangles formed with $n$ points in a plane,no three of which are collinear,and if $t_{n+1}-t_n=36$,then $n$ is equal to

Two blocks of masses $1 ~kg$ and $2 ~kg$ are connected by a metal wire going over a smooth pulley as shown in the figure. The breaking stress of the metal is $2 \times 10^9 ~N/m^2$. What should be the minimum radius of the wire used if it is not to break? Take $g = 10 ~m/s^2$.

Match the following genes of the $Lac$ operon with their respective products:
List-$I$ (Gene) | List-$II$ (Product)
$(i)$ $i$ gene | $(1)$ $\beta$-galactosidase
$(ii)$ $z$ gene | $(2)$ Permease
$(iii)$ $y$ gene | $(3)$ Repressor
$(iv)$ $a$ gene | $(4)$ Transacetylase
Select the correct option.

The right atrium of the human heart receives blood from which of the following?

For $k=1, 2, 3$,the box $B_k$ contains $k$ red balls and $(k+1)$ white balls. Let $P(B_1) = \frac{1}{2}$,$P(B_2) = \frac{1}{3}$,and $P(B_3) = \frac{1}{6}$. $A$ box is selected at random and a ball is drawn from it. If a red ball is drawn,then the probability that it has come from box $B_2$ is: