Air flows at the rate of $1.5 \: m^3/s$ through a horizontal pipe with a gradually reducing cross-section as shown in the figure. The two cross-sections of the pipe have diameters of the $400 \: mm$ and $200 \: mm$. Take the air density as $1.2 \: kg/m^3$ and assume inviscid incompressible flow. The change in pressure $(p_2-p_1)$ (in $kPa$) between sections $1$ and $2$ is

1. $-1.28$
2. $2.56$
3. $- 2.13$
4. $1.28$