11.

Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual?

What is an ecosystem?

An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror.

What is sustainable management? Why is reuse considered better in comparison to recycle ?

Management of forest and wild life resources is a very challenging task. Why ? Give any two reasons.

Two carbon compounds X and Y have the molecular formula C₄H₈ and C₅H₁₂ respectively. Which one of these is most likely to show addition reaction? Justify your answer. Also, give the chemical equation to explain the process of addition reaction in this case.

Complete the following chemical equations:
(i) CH₃COOC₂H₅+NaOH →
(ii) CH₃COOH+NaOH →
(iii) C₂H₅OH+CH₃COOH  

Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in the above two cases.

An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving the reason :
Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound formed when P reacts with Q.

What happens when :
Accidently, Planaria gets cut into many pieces?