Atoms and Molecules — Science STD 9 — Question

In a sample of ethyl ethanoate (CH₃COOC₂H₅) the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

A liquid is found to scatter a beam of light but leaves no residue when passed through the filter paper. The liquid can be described as:

A key of mechanical piano is first struck gently and then struck again but much harder this time. In the second case:

Health deals with:

1. Social well being.
2. Physical fitness.
3. Mental fitness.
4. All the above.

Which one of the following is a correct electronic configuration of sodium?

Rusting of an article made up of iron is called:

A motorcycle and a car start from rest at the same place at the same time and travel in the same direction.The motorcycle accelerates uniformly at 1m/ s² up to a speed of 36km/ h and the car at  0.5m/ s² up to a speed of 54km/ h.Then the distance at which the car overtakes the cycle-

When we change a feeble sound to a loud sound, we increase its:

_________ is used as a colouring agent to colour the slide which is to be observed under the microscope.

Elements having valency ‘one’ are:

1. Always metals.
2. Always non-metals.
3. Always metalloids.
4. Either metals or non-metals.