Solder is an alloy of lead and tin. It has a:
A. Low melting point and is used for welding electrical wires together.

B. Low melting point and is used for welding heavy iron machinery.

C. High melting point and is used for welding electrical wires together.

D. High melting point and is used for welding heavy iron machinery.

Explain the following statements:

i. Most metal oxides are insoluble in water but some of these dissolve in water. What are these oxides and their solutions in water called?

ii. At ordinary temperature, the surface of metals such as magnesium, aluminium and zinc, etc. is covered with a then layer. What is the composition of this layer? State its importance.

iii. Some alkali metals can be cut with a knife.

Why sodium chloride has high melting point?

Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?

(i) Au

(ii) Cu

(iii) Na

(iv) K

Stainless steel is very useful material for our life. In stainless steel, iron is mixed with

Silver articles become black on prolonged exposure to air. This is due to the formation of