On what basis are the three types of lichens classified?

$A$ radioactive material decays by simultaneous emission of two particles with respective half-lives $1620 \, years$ and $810 \, years$. The time (in years) after which one-fourth of the material remains is:

$A$ mass $M$ hangs on a massless rod of length $l$ which rotates at a constant angular frequency. The mass $M$ moves with steady speed in a circular path of constant radius. Assume that the system is in steady circular motion with constant angular velocity $\omega$. The angular momentum of $M$ about point $A$ is $L_A$ which lies in the positive $z$ direction and the angular momentum of $M$ about $B$ is $L_B$. The correct statement for this system is

A linear octasaccharide $($molar mass $=1024 g mol ^{-1} )$ on complete hydrolysis produces three monosaccharides: ribose, $2-$deoxyribose and glucose. The amount of $2-$deoxyribose formed is $58.26 \%( w / w )$ of the total amount of the monosaccharides produced in the hydrolyzed products. The number of ribose unit$(s)$ present in one molecule of octasaccharide is $.....$
Use : Molar mass $($in g $mol ^{-1} )$: ribose $=150,2-$deoxyribose $=134$, glucose $=180$; Atomic mass $($in amu$): H =1, O =16$

$A$ plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches $30^o$,the box starts to slip and slides $4.0\, m$ down the plank in $4.0\, s$. The coefficients of static and kinetic friction between the box and the plank will be,respectively:

If the curves $y^2 = 6x$ and $9x^2 + by^2 = 16$ intersect each other at right angles,then the value of $b$ is: