Persistent nucellus in the seed is known as

An element $P$ has atomic number $56$. What will be the formula of its halide?

$A$ square is inscribed in the circle $x^{2} + y^{2} - 2x + 4y - 93 = 0$ such that its sides are parallel to the coordinate axes. The coordinates of its vertices are:

$DDT$ residues are rapidly passed through food chains causing biomagnification. What is the reason for this?

Which of the following compounds when heated with $CO$ at $150^{\circ} C$ and $500 \ atm$ pressure in the presence of $BF_3$ forms ethyl propionate?

Which one of the following gases can deplete the ozone layer in the upper atmosphere?