81 Which of the following forms the basis of the modern periodic table?

82 How many periods and groups are present in the periodic table?

83 Arteries and veins are connected by a network of extremely narrow tubes called:

84 Which among the following is necessary to carry out the blood coagulation in a cut or wound?

85 an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed at a distance of 19 cm from the lens, the image formed is slightly larger than the object. The approximate focal length of the lens is:

86 A lens of focal length 12 cm forms an erect image, three times the size of the object. The distance between the object and image is:

87 A ray of light is travelling in a direction perpendicular to the boundary of a parallel glass slab. The ray of light:

88 Two big mirrors A and B are fitted side by side on a wall. A man is standing at such a distance from the wall that he can see the erect image of his face in both the mirrors. When the man starts walking towards the mirrors, he finds that the size of his face in mirror A goes on increasing but that in mirror B remains the same:

89 A concave mirror produces a magnification of +4. The object is placed:

90 A got his eye tested. The optician’s prescription for the spectacles was: Left eye: −3 D Right eye: −3.50 D The person is having a defect of vision called: