Which image does not form on a screen ?

A thin converging lens of focal length f= 25 cm forms the image of an object on a screen placed at a distance of 75 cm from the lens. The screen is moved closer to the lens by a distance of 25 cm. The distance through which the object has to be shifted, so that its image on the screen in sharp again is

Which element does not form amalgam and is used to store mercury?

Which does not form a Pentahalide?

Which of the following does not form Grignard reagent :

In an ecperiment to determine the focal length of a convex, lens a student obtained a sharp inverted image of a distant tree on the screen behind the lens. She then removed the screen and looked throught the lens in the direction of the object she will see

A screen is placed 90 cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20 cm. Determine the focal length of the lens.