Evaporation of a material takes place __________

Cloud is an example of ___________

Choose the correct statement

Calcium has 20 electrons.These K, L, M and N shells.Which shell or shells are incomplete?

Ribosomes are the centre for

Rate of evaporation increases with ......... of the vessel.

A mixture of mustard oil and water can be separated by .............

The cells which do not have membrane-bound organelle are called ...........................cells.

The three types of simple tissues are ..........., collenchyma and ................

Ligament and bone are example of ............... tissue.

(a) What temperature in Kelvin scale is equal to \(50°C\)?
(b) Describe an activity to show that rate of evaporation increases with surface area.
(c) State two differences between evaporation and boiling.

Give an example of i) a liquid diffusing into a solid, ii) solid diffusing into a liquid and iii) Solid diffusing into a solid.

Classify the following materials according to the state in which they exist around us:
Steel, blood, air, oil, rubber, honey, carbon dioxide, kerosene, LPG, CNG, nitrogen, oxygen, glass.

Arrange the following in the increasing order of: Iron nail, Kerosene, Oxygen.
(i) Force of attraction
(ii) Intermolecular space

Give reasons for the following:
(a) Water at room temperature is a liquid.
(b) a gas cylinder cannot be half filled.

Give reasons:
(a) Naphthalene balls disappear with time without leaving any solid.
(b) A gas exerts pressure on the walls of the container.

Convert the following temperature to Celsius scale:
(a) 300 k     (b) 573 K

List the various types of homogeneous and heterogeneous mixtures with examples.

(a) A solution is prepared by dissolving 15 g sodium chloride in 200 g of H₂O What is the mass by mass percentage of NaCL in this solution?
(b) What is solute and solvent in aerated drinks?

What is Tyndall effect? "Tyndall effect can be observed when sunlight passes through the canopy of dense forest." Explain, how this occurs?

Crystallisation is a better technique than simple evaporation. Give one reason to justify the statement.

Classify the following as element and compound:
(i) Silver  
(ii) Methane
(iii) Water
(iv) Mercury.

Which separation techniques will you apply for the separation of the following?
(a) sodium chloride from its solution in water
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small piece of metal in the engine oil of a car 
(d) Different pigments from an extract of flower petals.
(e) butter from curd
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine grains from husk.

A mixture is a combination of two or more substances that are not chemically united and do not exist in fixed proportions to each other.It can be physically separated into pure compounds or elements.Suppose you have a mixture of water, oil, iron filings and sulphur.
What steps you will take to separate the constituents of this mixture which are compounds and which are elements.

Can you make a distinction between a molecule and a compound?

What do the following formulae stand for:
(i) 2O (ii) O₂ (iii) O₃ (iv) H₂O

The mass of a single atom M is 3.05 x 10^-23 g.What is its atomic weight?What would this element be? Check table for possible answers.

What is the mass of 10 moles of sodium sulphite (Na₂SO₃)

What is the mass of 0.5 mole of water molecules?

What happens when the cathode rays are passed through an electric field between to parallel plates?Can one determine the nature of charge of the particles constituting the cathode rays from this experiment? If so how?

Describe the essential features of the model of atom proposed by E.Rutjherford.How is it different from that proposed by J.J Thomson?

Answer the following questions:
(a) Give the electronic distribution of element B
(b) The valency of element A
(c) The atomic number of element B.
(d) The mass number of element D.

Na⁺ has completely filled K and L shells. Explain.

How does an Amoeba obtain its food?

Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.