Five elements $A, B, C, D$ and $E$ have work functions $1.2\, eV, 2.4\, eV, 3.6\, eV, 4.8\, eV$ and $6\, eV$ respectively. If light of wavelength $4000\, \mathring{A}$ is allowed to fall on these elements,then photoelectrons are emitted by

In a floral formula,what does the notation $(K)$ denote?

Read the following five statements $(1-5)$ carefully and answer the question that follows.
$(1)$ In $Equisetum$,the female gametophyte is retained on the parent sporophyte.
$(2)$ In $Ginkgo$,the male gametophyte is not independent.
$(3)$ The sporophyte of $Polytrichum$ is more developed than that of $Riccia$.
$(4)$ Sexual reproduction in $Volvox$ is isogamous.
$(5)$ Spores of slime molds lack a cell wall.
How many of the above statements are correct?

If all the seven letters of the word $LEADING$ are permuted in all possible ways and the words thus formed are arranged as in the dictionary order,then the word in $2017^{\text{th}}$ place is

Three rings each of mass $M$ and radius $R$ are arranged as shown in the figure. The moment of inertia of the system about $YY'$ will be

The permissible use of the technique amniocentesis is for