Questions

- Send the box with the lock to Alex. 

- Alex can't open it, but can put another lock on the box. 

- Alex sends this box with the 2 locks back to you, you unlock your lock and send it back to Alex again.

- So there is just Alex's lock on the box and Alex can now open it.

The persons with 'O' blood group do not have antigens in the red corpuscles. So that blood will not cause agglutination of corpuscles if mixed with any type of blood. So group 'O' persons are called universal donors.

The Von Hippel Award, the Materials Research Society's highest honor, recognizes those qualities most prized by materials scientists and engineers—brilliance and originality of intellect, combined with vision that transcends the boundaries of conventional scientific disciplines. The Von Hippel Award is named after Arthur von Hippel (1898-2003), who was a pioneer in the study of dielectrics, semiconductors, ferromagnetics and ferroelectrics.

Eminent Scientist and Bharat Ratna Prof C.N.R. Rao was awarded 2017 Von Hippel Award. He is first Indian and first Asian to win this honour. The award will be presented to Prof Rao for his interdisciplinary contributions to development of novel functional materials, including nanomaterials, graphene, superconductivity, 2D materials and colossal magnetoresistance at Boston in November 2017.

Allotropes are the different physical forms of an element. Here in the given options, diamond and graphite are the pair of allotropes of carbon.

Some more examples are Molecular oxygen and ozone are pair of allotropes, Black and red phosphorous are also pairs of allotropes.