Through which cell of the embryo sac does the pollen tube enter the embryo sac?

$A$ person with blood group $AB$ is considered a universal recipient because they have:

Two uniform strings $A$ and $B$ made of steel are made to vibrate under the same tension. If the first overtone of $A$ is equal to the second overtone of $B$ and if the radius of $A$ is twice that of $B$,the ratio of the lengths of the strings is :

Which of the following complex ions is not expected to absorb visible light?

Which of the following is concerned with eubacteria?
$(1)$ Methanogens $(2)$ Anabaena $(3)$ $N_2$ fixation $(4)$ Thermoacidophiles $(5)$ Eukaryotes $(6)$ Diatoms $(7)$ Gelatinous sheath $(8)$ Heterocyst

$G-6-P$ dehydrogenase deficiency is associated with haemolysis of: