Which of the following is a Dobereiner's triad?

Match the following columns and select the correct option:

Column-$I$	Column-$II$
$(a)$ Floating ribs	$(i)$ Located between $2^{nd}$ and $7^{th}$ ribs
$(b)$ Acromion process	$(ii)$ Head of humerus
$(c)$ Scapula	$(iii)$ Clavicle articulation
$(d)$ Glenoid cavity	$(iv)$ Do not connect with the sternum

$(a)\quad(b)\quad(c)\quad(d)$

The phase difference between two waves,represented by $y_1 = 10^{-6} \sin \{100t + (x/50) + 0.5\} \ m$ and $y_2 = 10^{-6} \cos \{100t + (x/50)\} \ m$,where $x$ is in meters and $t$ is in seconds,is approximately .... $radians$.

Which of the following types of intercellular junctions helps in the passage of small molecules and ions?

The points of intersection of the perpendicular tangents drawn to the ellipse $4x^2 + 9y^2 = 36$ lie on the curve: