Why should a magnesium ribbon be cleared before burning in air?
Magnesium ribbon is cleaned because magnesium react with atmospheric oxygen and CO2 form stable compound. i.e. magnesium oxide & magnesium carbonate which causes hinderance in burning.
2Mg + O2 ----→ 2MgO
Magnesium Oxygen Magnesium oxide
When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Outline a project which aims to find the dominant coat colour in dogs.
Draw the structure for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
How is the sex of the child determined in human beings?
(a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Calculate the number of electrons constituting one coulomb of charge.
What is an homologous series? Explain with an example.
Why is variation beneficial to the species but not necessarily for the individual?
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
What do you mean by a precipitation reaction? Explain by giving examples.
Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
What is a balanced chemical equation? Why should chemical equations be balanced?
A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south (b) towards east
(c) downward (d) upward
Can any source of energy be pollution-free? Why or why not?
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
State Fleming’s left-hand rule.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
What are the components of the transport system in highly organised plants?
Explain the terms analogous and homologous organs with examples.